A simple way to obtain $prod_{pinmathbb{P}}frac{1}{1-p^{-s}}=sum_{n=1}^{infty}frac{1}{n^s}$.












26












$begingroup$


Let $ p_1<p_2 <cdots <p_k < cdots $ the increasing list in set $mathbb{P}$ of all prime numbers .
By sum of infinite geometric series we have $sum_{k=0}^infty r^k = frac{1}{1-r}$, for $0<r<1$. For all $s>1$ and $r=frac{1}{p_k^{s}}$ we have
$$
begin{array}{cccccc}
dfrac{1}{1-p_{1}^{-s}}
&
=
&
1+dfrac{1}{(p_1^s)^1}+dfrac{1}{(p_1^s)^2}+dfrac{1}{(p_1^s)^3}+
&
!!cdots!!
&
+dfrac{1}{(p_1^{s})^{alpha_1}}+
&
cdots
\
dfrac{1}{1-p_{2}^{-s}}
&
=
&
1+dfrac{1}{(p_2^s)^1}+dfrac{1}{(p_2^s)^2}+dfrac{1}{(p_2^s)^3}+
&
!!cdots!!
&
+dfrac{1}{(p_2^s)^{alpha_2}}+
&
cdots
\
dfrac{1}{1-p_{3}^{-s}}
&
=
&
1+dfrac{1}{(p_3^s)^1}+dfrac{1}{(p_3^s)^2}+dfrac{1}{(p_3^s)^3}+
&
!!cdots!!
&
+dfrac{1}{(p_3^s)^{alpha_3}}+
&
cdots
\
vdots
&
vdots
&
vdots
&
vdots
&
vdots
&vdots
\
\
vdots
&
vdots
&
vdots
&
vdots
&
vdots
&
vdots
\
dfrac{1}{1-p_{k}^{-s}}
&
=
&
1+dfrac{1}{(p_k^s)^1}+dfrac{1}{(p_k^s)^2}+dfrac{1}{(p_k^s)^3}+
&
!!cdots!!
&
+dfrac{1}{(p_k^s)^{alpha_k}}+
&
cdots
\
vdots
&
vdots
&
vdots
&
vdots
&
vdots
&
vdots
\
end{array}
$$



And the Fundamental Theorem of Arithmetic tells us that every integer $ n> 1$ can be decomposed uniquely as a product
$$
n= p_{i_1}^{alpha_{i_1}}p_{i_2}^{alpha_{i_2}}cdots p_{i_k}^{alpha_{i_k}}
$$

of powers of prime numbers $p_{i_1}< p_{i_2}< cdots < p_{i_k}$ for integers $alpha_{i_1},alpha_{i_2},ldots,alpha_{i_k}geq 1$. Since $
n^s= (p_{i_1}^s)^{alpha_{i_1}}(p_{i_2}^{s})^{alpha_{i_2}}cdots (p_{i_k}^s)^{alpha_{i_k}}$
and
using brute force with I can prove that
$$
prod_{pinmathbb{P}}frac{1}{1-p^{-s}}=sum_{n=1}^infty frac{1}{n^s}
$$

But I would like to know if there is a simple and elegant way to achieve this result is up through the above list.










share|cite|improve this question











$endgroup$








  • 1




    $begingroup$
    Heres a fantastic video/playlist that talks about the Euler product youtube.com/…
    $endgroup$
    – Fede Poncio
    Dec 10 '15 at 4:11


















26












$begingroup$


Let $ p_1<p_2 <cdots <p_k < cdots $ the increasing list in set $mathbb{P}$ of all prime numbers .
By sum of infinite geometric series we have $sum_{k=0}^infty r^k = frac{1}{1-r}$, for $0<r<1$. For all $s>1$ and $r=frac{1}{p_k^{s}}$ we have
$$
begin{array}{cccccc}
dfrac{1}{1-p_{1}^{-s}}
&
=
&
1+dfrac{1}{(p_1^s)^1}+dfrac{1}{(p_1^s)^2}+dfrac{1}{(p_1^s)^3}+
&
!!cdots!!
&
+dfrac{1}{(p_1^{s})^{alpha_1}}+
&
cdots
\
dfrac{1}{1-p_{2}^{-s}}
&
=
&
1+dfrac{1}{(p_2^s)^1}+dfrac{1}{(p_2^s)^2}+dfrac{1}{(p_2^s)^3}+
&
!!cdots!!
&
+dfrac{1}{(p_2^s)^{alpha_2}}+
&
cdots
\
dfrac{1}{1-p_{3}^{-s}}
&
=
&
1+dfrac{1}{(p_3^s)^1}+dfrac{1}{(p_3^s)^2}+dfrac{1}{(p_3^s)^3}+
&
!!cdots!!
&
+dfrac{1}{(p_3^s)^{alpha_3}}+
&
cdots
\
vdots
&
vdots
&
vdots
&
vdots
&
vdots
&vdots
\
\
vdots
&
vdots
&
vdots
&
vdots
&
vdots
&
vdots
\
dfrac{1}{1-p_{k}^{-s}}
&
=
&
1+dfrac{1}{(p_k^s)^1}+dfrac{1}{(p_k^s)^2}+dfrac{1}{(p_k^s)^3}+
&
!!cdots!!
&
+dfrac{1}{(p_k^s)^{alpha_k}}+
&
cdots
\
vdots
&
vdots
&
vdots
&
vdots
&
vdots
&
vdots
\
end{array}
$$



And the Fundamental Theorem of Arithmetic tells us that every integer $ n> 1$ can be decomposed uniquely as a product
$$
n= p_{i_1}^{alpha_{i_1}}p_{i_2}^{alpha_{i_2}}cdots p_{i_k}^{alpha_{i_k}}
$$

of powers of prime numbers $p_{i_1}< p_{i_2}< cdots < p_{i_k}$ for integers $alpha_{i_1},alpha_{i_2},ldots,alpha_{i_k}geq 1$. Since $
n^s= (p_{i_1}^s)^{alpha_{i_1}}(p_{i_2}^{s})^{alpha_{i_2}}cdots (p_{i_k}^s)^{alpha_{i_k}}$
and
using brute force with I can prove that
$$
prod_{pinmathbb{P}}frac{1}{1-p^{-s}}=sum_{n=1}^infty frac{1}{n^s}
$$

But I would like to know if there is a simple and elegant way to achieve this result is up through the above list.










share|cite|improve this question











$endgroup$








  • 1




    $begingroup$
    Heres a fantastic video/playlist that talks about the Euler product youtube.com/…
    $endgroup$
    – Fede Poncio
    Dec 10 '15 at 4:11
















26












26








26


29



$begingroup$


Let $ p_1<p_2 <cdots <p_k < cdots $ the increasing list in set $mathbb{P}$ of all prime numbers .
By sum of infinite geometric series we have $sum_{k=0}^infty r^k = frac{1}{1-r}$, for $0<r<1$. For all $s>1$ and $r=frac{1}{p_k^{s}}$ we have
$$
begin{array}{cccccc}
dfrac{1}{1-p_{1}^{-s}}
&
=
&
1+dfrac{1}{(p_1^s)^1}+dfrac{1}{(p_1^s)^2}+dfrac{1}{(p_1^s)^3}+
&
!!cdots!!
&
+dfrac{1}{(p_1^{s})^{alpha_1}}+
&
cdots
\
dfrac{1}{1-p_{2}^{-s}}
&
=
&
1+dfrac{1}{(p_2^s)^1}+dfrac{1}{(p_2^s)^2}+dfrac{1}{(p_2^s)^3}+
&
!!cdots!!
&
+dfrac{1}{(p_2^s)^{alpha_2}}+
&
cdots
\
dfrac{1}{1-p_{3}^{-s}}
&
=
&
1+dfrac{1}{(p_3^s)^1}+dfrac{1}{(p_3^s)^2}+dfrac{1}{(p_3^s)^3}+
&
!!cdots!!
&
+dfrac{1}{(p_3^s)^{alpha_3}}+
&
cdots
\
vdots
&
vdots
&
vdots
&
vdots
&
vdots
&vdots
\
\
vdots
&
vdots
&
vdots
&
vdots
&
vdots
&
vdots
\
dfrac{1}{1-p_{k}^{-s}}
&
=
&
1+dfrac{1}{(p_k^s)^1}+dfrac{1}{(p_k^s)^2}+dfrac{1}{(p_k^s)^3}+
&
!!cdots!!
&
+dfrac{1}{(p_k^s)^{alpha_k}}+
&
cdots
\
vdots
&
vdots
&
vdots
&
vdots
&
vdots
&
vdots
\
end{array}
$$



And the Fundamental Theorem of Arithmetic tells us that every integer $ n> 1$ can be decomposed uniquely as a product
$$
n= p_{i_1}^{alpha_{i_1}}p_{i_2}^{alpha_{i_2}}cdots p_{i_k}^{alpha_{i_k}}
$$

of powers of prime numbers $p_{i_1}< p_{i_2}< cdots < p_{i_k}$ for integers $alpha_{i_1},alpha_{i_2},ldots,alpha_{i_k}geq 1$. Since $
n^s= (p_{i_1}^s)^{alpha_{i_1}}(p_{i_2}^{s})^{alpha_{i_2}}cdots (p_{i_k}^s)^{alpha_{i_k}}$
and
using brute force with I can prove that
$$
prod_{pinmathbb{P}}frac{1}{1-p^{-s}}=sum_{n=1}^infty frac{1}{n^s}
$$

But I would like to know if there is a simple and elegant way to achieve this result is up through the above list.










share|cite|improve this question











$endgroup$




Let $ p_1<p_2 <cdots <p_k < cdots $ the increasing list in set $mathbb{P}$ of all prime numbers .
By sum of infinite geometric series we have $sum_{k=0}^infty r^k = frac{1}{1-r}$, for $0<r<1$. For all $s>1$ and $r=frac{1}{p_k^{s}}$ we have
$$
begin{array}{cccccc}
dfrac{1}{1-p_{1}^{-s}}
&
=
&
1+dfrac{1}{(p_1^s)^1}+dfrac{1}{(p_1^s)^2}+dfrac{1}{(p_1^s)^3}+
&
!!cdots!!
&
+dfrac{1}{(p_1^{s})^{alpha_1}}+
&
cdots
\
dfrac{1}{1-p_{2}^{-s}}
&
=
&
1+dfrac{1}{(p_2^s)^1}+dfrac{1}{(p_2^s)^2}+dfrac{1}{(p_2^s)^3}+
&
!!cdots!!
&
+dfrac{1}{(p_2^s)^{alpha_2}}+
&
cdots
\
dfrac{1}{1-p_{3}^{-s}}
&
=
&
1+dfrac{1}{(p_3^s)^1}+dfrac{1}{(p_3^s)^2}+dfrac{1}{(p_3^s)^3}+
&
!!cdots!!
&
+dfrac{1}{(p_3^s)^{alpha_3}}+
&
cdots
\
vdots
&
vdots
&
vdots
&
vdots
&
vdots
&vdots
\
\
vdots
&
vdots
&
vdots
&
vdots
&
vdots
&
vdots
\
dfrac{1}{1-p_{k}^{-s}}
&
=
&
1+dfrac{1}{(p_k^s)^1}+dfrac{1}{(p_k^s)^2}+dfrac{1}{(p_k^s)^3}+
&
!!cdots!!
&
+dfrac{1}{(p_k^s)^{alpha_k}}+
&
cdots
\
vdots
&
vdots
&
vdots
&
vdots
&
vdots
&
vdots
\
end{array}
$$



And the Fundamental Theorem of Arithmetic tells us that every integer $ n> 1$ can be decomposed uniquely as a product
$$
n= p_{i_1}^{alpha_{i_1}}p_{i_2}^{alpha_{i_2}}cdots p_{i_k}^{alpha_{i_k}}
$$

of powers of prime numbers $p_{i_1}< p_{i_2}< cdots < p_{i_k}$ for integers $alpha_{i_1},alpha_{i_2},ldots,alpha_{i_k}geq 1$. Since $
n^s= (p_{i_1}^s)^{alpha_{i_1}}(p_{i_2}^{s})^{alpha_{i_2}}cdots (p_{i_k}^s)^{alpha_{i_k}}$
and
using brute force with I can prove that
$$
prod_{pinmathbb{P}}frac{1}{1-p^{-s}}=sum_{n=1}^infty frac{1}{n^s}
$$

But I would like to know if there is a simple and elegant way to achieve this result is up through the above list.







real-analysis number-theory probability-theory prime-numbers independence






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Feb 14 at 13:50







MathOverview

















asked Jun 24 '13 at 0:11









MathOverviewMathOverview

8,69243164




8,69243164








  • 1




    $begingroup$
    Heres a fantastic video/playlist that talks about the Euler product youtube.com/…
    $endgroup$
    – Fede Poncio
    Dec 10 '15 at 4:11
















  • 1




    $begingroup$
    Heres a fantastic video/playlist that talks about the Euler product youtube.com/…
    $endgroup$
    – Fede Poncio
    Dec 10 '15 at 4:11










1




1




$begingroup$
Heres a fantastic video/playlist that talks about the Euler product youtube.com/…
$endgroup$
– Fede Poncio
Dec 10 '15 at 4:11






$begingroup$
Heres a fantastic video/playlist that talks about the Euler product youtube.com/…
$endgroup$
– Fede Poncio
Dec 10 '15 at 4:11












2 Answers
2






active

oldest

votes


















29












$begingroup$

I absolutely love this result, I literally cannot stop from getting goosebumps and smiling whenever I think about it. It is a proof from probability theory! I learned it in David William's Probability with Martingales, of which it is part of exercise E4.2.



Fix $s>1$ and recall that $zeta(s) = sum_{n in mathbb{N}} n^{-s}$, so we aim to show that $1/zeta(s) = prod_p(1-p^{-s})$ where of course $p$ ranges over the primes.



First, define a probability measure $P$ and an $mathbb{N}$-valued random variable $X$ such that $P(X=n) = n^{-s}/zeta(s)$ (for example take $P({n}) = n^{-s}/zeta(s)$ and $X(omega)=omega$). Let $E_k := {X text{ is divisible by } k}$. We claim that the events $(E_p : p text{ prime})$ are independent. We note that
$$
P(E_k) = sum_{i=1}^infty P(X=ik) = sum_{i=1}^infty frac{(ik)^{-s}}{zeta(s)} = k^{-s} frac{zeta(s)}{zeta(s)} = k^{-s}.
$$



Then if $p_1,ldots,p_n$ are distinct primes we have $$bigcap_{i=1}^n E_{p_i} = E_{prod_{i=1}^np_i},$$ so that
$$
Pleft(bigcap_{i=1}^n E_{p_i}right) = P(E_{prod_{i=1}^np_i}) = left(prod_{i=1}^n p_i right)^{-s} = prod_{i=1}^n p_i^{-s} = prod_{i=1}^n P(E_{p_i})
$$
so our independence claim is proved.
Then we note that $1$ is the unique positive integer which is not a multiple of any prime. Hence
$$
frac{1}{zeta(s)} = P(X=1) = Pleft(bigcap_p E_p^cright) = prod_p(1-P(E_p)) = prod_p(1-p^{-s}).
$$






share|cite|improve this answer











$endgroup$









  • 4




    $begingroup$
    This is indeed a cool proof! Picky point: how does one justify the independence of infinitely many events (used in the last line) when one has shown only independence of finitely many events?
    $endgroup$
    – Greg Martin
    Jun 28 '13 at 3:48






  • 2




    $begingroup$
    @GregMartin Independence of an infinite collection is defined to mean every finite subcollection is independent (which I did show). Then we have $$P(cap_p E^c_p) = P(cap_n cap_{p leq n} E^c_p) = lim_n P(cap_{p leq n} E^c_p) = lim_n prod_{p leq n} (1-P(E_p)) = prod_p(1-p^{-s}).$$ Of course $p$ ranges over primes and $n$ ranges over natural numbers (should be clear by context).
    $endgroup$
    – nullUser
    Jun 28 '13 at 4:02








  • 1




    $begingroup$
    Note that one never has to worry about convergence of products of probabilities because $a_n := prod_{i=1}^n P[cdots]$ is a monotone (decreasing) sequence bounded below by $0$, this is why I left out my previous comment from my original argument.
    $endgroup$
    – nullUser
    Jun 28 '13 at 4:11








  • 1




    $begingroup$
    @nullUser Congratulations to replicate here this fantastic race. It displays a fantastic correspondence between primality of numbers and independence of measurable sets.
    $endgroup$
    – MathOverview
    Jul 3 '13 at 15:40






  • 2




    $begingroup$
    @ThomasAndrews What part confuses you? Make sure to read my comment above.
    $endgroup$
    – nullUser
    Jul 3 '13 at 19:57



















4












$begingroup$

Let $s$ for which $Re(s)>1$ then, for all $p in mathbb{P}$ we have $$sum_{k=1}^{infty} frac{1}{p^{ks}}=left(1-frac{1}{p^s}right)^{-1}$$



Now let $A(N)$ be the set of all strictly positive numbers such as all prime divisors are at maximum $N$.



Then $$prod_{p in mathbb{P},text{ }p<N}left(1-frac{1}{p^s}right)^{-1}=sum_{n in A(N)}frac{1}{n^s}$$



Obviously ${1,...,N}subset A(N)$, then



$$left|zeta(s)-prod_{p in mathbb{P},text{ }p<N}left(1-frac{1}{p^s}right)^{-1}right|le sum_{n>N}frac{1}{n^{Re{(s)}}}$$



When $N$ goes to infinity it gives the result.






share|cite|improve this answer









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    2 Answers
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    2 Answers
    2






    active

    oldest

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    active

    oldest

    votes






    active

    oldest

    votes









    29












    $begingroup$

    I absolutely love this result, I literally cannot stop from getting goosebumps and smiling whenever I think about it. It is a proof from probability theory! I learned it in David William's Probability with Martingales, of which it is part of exercise E4.2.



    Fix $s>1$ and recall that $zeta(s) = sum_{n in mathbb{N}} n^{-s}$, so we aim to show that $1/zeta(s) = prod_p(1-p^{-s})$ where of course $p$ ranges over the primes.



    First, define a probability measure $P$ and an $mathbb{N}$-valued random variable $X$ such that $P(X=n) = n^{-s}/zeta(s)$ (for example take $P({n}) = n^{-s}/zeta(s)$ and $X(omega)=omega$). Let $E_k := {X text{ is divisible by } k}$. We claim that the events $(E_p : p text{ prime})$ are independent. We note that
    $$
    P(E_k) = sum_{i=1}^infty P(X=ik) = sum_{i=1}^infty frac{(ik)^{-s}}{zeta(s)} = k^{-s} frac{zeta(s)}{zeta(s)} = k^{-s}.
    $$



    Then if $p_1,ldots,p_n$ are distinct primes we have $$bigcap_{i=1}^n E_{p_i} = E_{prod_{i=1}^np_i},$$ so that
    $$
    Pleft(bigcap_{i=1}^n E_{p_i}right) = P(E_{prod_{i=1}^np_i}) = left(prod_{i=1}^n p_i right)^{-s} = prod_{i=1}^n p_i^{-s} = prod_{i=1}^n P(E_{p_i})
    $$
    so our independence claim is proved.
    Then we note that $1$ is the unique positive integer which is not a multiple of any prime. Hence
    $$
    frac{1}{zeta(s)} = P(X=1) = Pleft(bigcap_p E_p^cright) = prod_p(1-P(E_p)) = prod_p(1-p^{-s}).
    $$






    share|cite|improve this answer











    $endgroup$









    • 4




      $begingroup$
      This is indeed a cool proof! Picky point: how does one justify the independence of infinitely many events (used in the last line) when one has shown only independence of finitely many events?
      $endgroup$
      – Greg Martin
      Jun 28 '13 at 3:48






    • 2




      $begingroup$
      @GregMartin Independence of an infinite collection is defined to mean every finite subcollection is independent (which I did show). Then we have $$P(cap_p E^c_p) = P(cap_n cap_{p leq n} E^c_p) = lim_n P(cap_{p leq n} E^c_p) = lim_n prod_{p leq n} (1-P(E_p)) = prod_p(1-p^{-s}).$$ Of course $p$ ranges over primes and $n$ ranges over natural numbers (should be clear by context).
      $endgroup$
      – nullUser
      Jun 28 '13 at 4:02








    • 1




      $begingroup$
      Note that one never has to worry about convergence of products of probabilities because $a_n := prod_{i=1}^n P[cdots]$ is a monotone (decreasing) sequence bounded below by $0$, this is why I left out my previous comment from my original argument.
      $endgroup$
      – nullUser
      Jun 28 '13 at 4:11








    • 1




      $begingroup$
      @nullUser Congratulations to replicate here this fantastic race. It displays a fantastic correspondence between primality of numbers and independence of measurable sets.
      $endgroup$
      – MathOverview
      Jul 3 '13 at 15:40






    • 2




      $begingroup$
      @ThomasAndrews What part confuses you? Make sure to read my comment above.
      $endgroup$
      – nullUser
      Jul 3 '13 at 19:57
















    29












    $begingroup$

    I absolutely love this result, I literally cannot stop from getting goosebumps and smiling whenever I think about it. It is a proof from probability theory! I learned it in David William's Probability with Martingales, of which it is part of exercise E4.2.



    Fix $s>1$ and recall that $zeta(s) = sum_{n in mathbb{N}} n^{-s}$, so we aim to show that $1/zeta(s) = prod_p(1-p^{-s})$ where of course $p$ ranges over the primes.



    First, define a probability measure $P$ and an $mathbb{N}$-valued random variable $X$ such that $P(X=n) = n^{-s}/zeta(s)$ (for example take $P({n}) = n^{-s}/zeta(s)$ and $X(omega)=omega$). Let $E_k := {X text{ is divisible by } k}$. We claim that the events $(E_p : p text{ prime})$ are independent. We note that
    $$
    P(E_k) = sum_{i=1}^infty P(X=ik) = sum_{i=1}^infty frac{(ik)^{-s}}{zeta(s)} = k^{-s} frac{zeta(s)}{zeta(s)} = k^{-s}.
    $$



    Then if $p_1,ldots,p_n$ are distinct primes we have $$bigcap_{i=1}^n E_{p_i} = E_{prod_{i=1}^np_i},$$ so that
    $$
    Pleft(bigcap_{i=1}^n E_{p_i}right) = P(E_{prod_{i=1}^np_i}) = left(prod_{i=1}^n p_i right)^{-s} = prod_{i=1}^n p_i^{-s} = prod_{i=1}^n P(E_{p_i})
    $$
    so our independence claim is proved.
    Then we note that $1$ is the unique positive integer which is not a multiple of any prime. Hence
    $$
    frac{1}{zeta(s)} = P(X=1) = Pleft(bigcap_p E_p^cright) = prod_p(1-P(E_p)) = prod_p(1-p^{-s}).
    $$






    share|cite|improve this answer











    $endgroup$









    • 4




      $begingroup$
      This is indeed a cool proof! Picky point: how does one justify the independence of infinitely many events (used in the last line) when one has shown only independence of finitely many events?
      $endgroup$
      – Greg Martin
      Jun 28 '13 at 3:48






    • 2




      $begingroup$
      @GregMartin Independence of an infinite collection is defined to mean every finite subcollection is independent (which I did show). Then we have $$P(cap_p E^c_p) = P(cap_n cap_{p leq n} E^c_p) = lim_n P(cap_{p leq n} E^c_p) = lim_n prod_{p leq n} (1-P(E_p)) = prod_p(1-p^{-s}).$$ Of course $p$ ranges over primes and $n$ ranges over natural numbers (should be clear by context).
      $endgroup$
      – nullUser
      Jun 28 '13 at 4:02








    • 1




      $begingroup$
      Note that one never has to worry about convergence of products of probabilities because $a_n := prod_{i=1}^n P[cdots]$ is a monotone (decreasing) sequence bounded below by $0$, this is why I left out my previous comment from my original argument.
      $endgroup$
      – nullUser
      Jun 28 '13 at 4:11








    • 1




      $begingroup$
      @nullUser Congratulations to replicate here this fantastic race. It displays a fantastic correspondence between primality of numbers and independence of measurable sets.
      $endgroup$
      – MathOverview
      Jul 3 '13 at 15:40






    • 2




      $begingroup$
      @ThomasAndrews What part confuses you? Make sure to read my comment above.
      $endgroup$
      – nullUser
      Jul 3 '13 at 19:57














    29












    29








    29





    $begingroup$

    I absolutely love this result, I literally cannot stop from getting goosebumps and smiling whenever I think about it. It is a proof from probability theory! I learned it in David William's Probability with Martingales, of which it is part of exercise E4.2.



    Fix $s>1$ and recall that $zeta(s) = sum_{n in mathbb{N}} n^{-s}$, so we aim to show that $1/zeta(s) = prod_p(1-p^{-s})$ where of course $p$ ranges over the primes.



    First, define a probability measure $P$ and an $mathbb{N}$-valued random variable $X$ such that $P(X=n) = n^{-s}/zeta(s)$ (for example take $P({n}) = n^{-s}/zeta(s)$ and $X(omega)=omega$). Let $E_k := {X text{ is divisible by } k}$. We claim that the events $(E_p : p text{ prime})$ are independent. We note that
    $$
    P(E_k) = sum_{i=1}^infty P(X=ik) = sum_{i=1}^infty frac{(ik)^{-s}}{zeta(s)} = k^{-s} frac{zeta(s)}{zeta(s)} = k^{-s}.
    $$



    Then if $p_1,ldots,p_n$ are distinct primes we have $$bigcap_{i=1}^n E_{p_i} = E_{prod_{i=1}^np_i},$$ so that
    $$
    Pleft(bigcap_{i=1}^n E_{p_i}right) = P(E_{prod_{i=1}^np_i}) = left(prod_{i=1}^n p_i right)^{-s} = prod_{i=1}^n p_i^{-s} = prod_{i=1}^n P(E_{p_i})
    $$
    so our independence claim is proved.
    Then we note that $1$ is the unique positive integer which is not a multiple of any prime. Hence
    $$
    frac{1}{zeta(s)} = P(X=1) = Pleft(bigcap_p E_p^cright) = prod_p(1-P(E_p)) = prod_p(1-p^{-s}).
    $$






    share|cite|improve this answer











    $endgroup$



    I absolutely love this result, I literally cannot stop from getting goosebumps and smiling whenever I think about it. It is a proof from probability theory! I learned it in David William's Probability with Martingales, of which it is part of exercise E4.2.



    Fix $s>1$ and recall that $zeta(s) = sum_{n in mathbb{N}} n^{-s}$, so we aim to show that $1/zeta(s) = prod_p(1-p^{-s})$ where of course $p$ ranges over the primes.



    First, define a probability measure $P$ and an $mathbb{N}$-valued random variable $X$ such that $P(X=n) = n^{-s}/zeta(s)$ (for example take $P({n}) = n^{-s}/zeta(s)$ and $X(omega)=omega$). Let $E_k := {X text{ is divisible by } k}$. We claim that the events $(E_p : p text{ prime})$ are independent. We note that
    $$
    P(E_k) = sum_{i=1}^infty P(X=ik) = sum_{i=1}^infty frac{(ik)^{-s}}{zeta(s)} = k^{-s} frac{zeta(s)}{zeta(s)} = k^{-s}.
    $$



    Then if $p_1,ldots,p_n$ are distinct primes we have $$bigcap_{i=1}^n E_{p_i} = E_{prod_{i=1}^np_i},$$ so that
    $$
    Pleft(bigcap_{i=1}^n E_{p_i}right) = P(E_{prod_{i=1}^np_i}) = left(prod_{i=1}^n p_i right)^{-s} = prod_{i=1}^n p_i^{-s} = prod_{i=1}^n P(E_{p_i})
    $$
    so our independence claim is proved.
    Then we note that $1$ is the unique positive integer which is not a multiple of any prime. Hence
    $$
    frac{1}{zeta(s)} = P(X=1) = Pleft(bigcap_p E_p^cright) = prod_p(1-P(E_p)) = prod_p(1-p^{-s}).
    $$







    share|cite|improve this answer














    share|cite|improve this answer



    share|cite|improve this answer








    edited Dec 12 '15 at 17:46









    Michael Hardy

    1




    1










    answered Jun 24 '13 at 1:09









    nullUsernullUser

    16.8k442106




    16.8k442106








    • 4




      $begingroup$
      This is indeed a cool proof! Picky point: how does one justify the independence of infinitely many events (used in the last line) when one has shown only independence of finitely many events?
      $endgroup$
      – Greg Martin
      Jun 28 '13 at 3:48






    • 2




      $begingroup$
      @GregMartin Independence of an infinite collection is defined to mean every finite subcollection is independent (which I did show). Then we have $$P(cap_p E^c_p) = P(cap_n cap_{p leq n} E^c_p) = lim_n P(cap_{p leq n} E^c_p) = lim_n prod_{p leq n} (1-P(E_p)) = prod_p(1-p^{-s}).$$ Of course $p$ ranges over primes and $n$ ranges over natural numbers (should be clear by context).
      $endgroup$
      – nullUser
      Jun 28 '13 at 4:02








    • 1




      $begingroup$
      Note that one never has to worry about convergence of products of probabilities because $a_n := prod_{i=1}^n P[cdots]$ is a monotone (decreasing) sequence bounded below by $0$, this is why I left out my previous comment from my original argument.
      $endgroup$
      – nullUser
      Jun 28 '13 at 4:11








    • 1




      $begingroup$
      @nullUser Congratulations to replicate here this fantastic race. It displays a fantastic correspondence between primality of numbers and independence of measurable sets.
      $endgroup$
      – MathOverview
      Jul 3 '13 at 15:40






    • 2




      $begingroup$
      @ThomasAndrews What part confuses you? Make sure to read my comment above.
      $endgroup$
      – nullUser
      Jul 3 '13 at 19:57














    • 4




      $begingroup$
      This is indeed a cool proof! Picky point: how does one justify the independence of infinitely many events (used in the last line) when one has shown only independence of finitely many events?
      $endgroup$
      – Greg Martin
      Jun 28 '13 at 3:48






    • 2




      $begingroup$
      @GregMartin Independence of an infinite collection is defined to mean every finite subcollection is independent (which I did show). Then we have $$P(cap_p E^c_p) = P(cap_n cap_{p leq n} E^c_p) = lim_n P(cap_{p leq n} E^c_p) = lim_n prod_{p leq n} (1-P(E_p)) = prod_p(1-p^{-s}).$$ Of course $p$ ranges over primes and $n$ ranges over natural numbers (should be clear by context).
      $endgroup$
      – nullUser
      Jun 28 '13 at 4:02








    • 1




      $begingroup$
      Note that one never has to worry about convergence of products of probabilities because $a_n := prod_{i=1}^n P[cdots]$ is a monotone (decreasing) sequence bounded below by $0$, this is why I left out my previous comment from my original argument.
      $endgroup$
      – nullUser
      Jun 28 '13 at 4:11








    • 1




      $begingroup$
      @nullUser Congratulations to replicate here this fantastic race. It displays a fantastic correspondence between primality of numbers and independence of measurable sets.
      $endgroup$
      – MathOverview
      Jul 3 '13 at 15:40






    • 2




      $begingroup$
      @ThomasAndrews What part confuses you? Make sure to read my comment above.
      $endgroup$
      – nullUser
      Jul 3 '13 at 19:57








    4




    4




    $begingroup$
    This is indeed a cool proof! Picky point: how does one justify the independence of infinitely many events (used in the last line) when one has shown only independence of finitely many events?
    $endgroup$
    – Greg Martin
    Jun 28 '13 at 3:48




    $begingroup$
    This is indeed a cool proof! Picky point: how does one justify the independence of infinitely many events (used in the last line) when one has shown only independence of finitely many events?
    $endgroup$
    – Greg Martin
    Jun 28 '13 at 3:48




    2




    2




    $begingroup$
    @GregMartin Independence of an infinite collection is defined to mean every finite subcollection is independent (which I did show). Then we have $$P(cap_p E^c_p) = P(cap_n cap_{p leq n} E^c_p) = lim_n P(cap_{p leq n} E^c_p) = lim_n prod_{p leq n} (1-P(E_p)) = prod_p(1-p^{-s}).$$ Of course $p$ ranges over primes and $n$ ranges over natural numbers (should be clear by context).
    $endgroup$
    – nullUser
    Jun 28 '13 at 4:02






    $begingroup$
    @GregMartin Independence of an infinite collection is defined to mean every finite subcollection is independent (which I did show). Then we have $$P(cap_p E^c_p) = P(cap_n cap_{p leq n} E^c_p) = lim_n P(cap_{p leq n} E^c_p) = lim_n prod_{p leq n} (1-P(E_p)) = prod_p(1-p^{-s}).$$ Of course $p$ ranges over primes and $n$ ranges over natural numbers (should be clear by context).
    $endgroup$
    – nullUser
    Jun 28 '13 at 4:02






    1




    1




    $begingroup$
    Note that one never has to worry about convergence of products of probabilities because $a_n := prod_{i=1}^n P[cdots]$ is a monotone (decreasing) sequence bounded below by $0$, this is why I left out my previous comment from my original argument.
    $endgroup$
    – nullUser
    Jun 28 '13 at 4:11






    $begingroup$
    Note that one never has to worry about convergence of products of probabilities because $a_n := prod_{i=1}^n P[cdots]$ is a monotone (decreasing) sequence bounded below by $0$, this is why I left out my previous comment from my original argument.
    $endgroup$
    – nullUser
    Jun 28 '13 at 4:11






    1




    1




    $begingroup$
    @nullUser Congratulations to replicate here this fantastic race. It displays a fantastic correspondence between primality of numbers and independence of measurable sets.
    $endgroup$
    – MathOverview
    Jul 3 '13 at 15:40




    $begingroup$
    @nullUser Congratulations to replicate here this fantastic race. It displays a fantastic correspondence between primality of numbers and independence of measurable sets.
    $endgroup$
    – MathOverview
    Jul 3 '13 at 15:40




    2




    2




    $begingroup$
    @ThomasAndrews What part confuses you? Make sure to read my comment above.
    $endgroup$
    – nullUser
    Jul 3 '13 at 19:57




    $begingroup$
    @ThomasAndrews What part confuses you? Make sure to read my comment above.
    $endgroup$
    – nullUser
    Jul 3 '13 at 19:57











    4












    $begingroup$

    Let $s$ for which $Re(s)>1$ then, for all $p in mathbb{P}$ we have $$sum_{k=1}^{infty} frac{1}{p^{ks}}=left(1-frac{1}{p^s}right)^{-1}$$



    Now let $A(N)$ be the set of all strictly positive numbers such as all prime divisors are at maximum $N$.



    Then $$prod_{p in mathbb{P},text{ }p<N}left(1-frac{1}{p^s}right)^{-1}=sum_{n in A(N)}frac{1}{n^s}$$



    Obviously ${1,...,N}subset A(N)$, then



    $$left|zeta(s)-prod_{p in mathbb{P},text{ }p<N}left(1-frac{1}{p^s}right)^{-1}right|le sum_{n>N}frac{1}{n^{Re{(s)}}}$$



    When $N$ goes to infinity it gives the result.






    share|cite|improve this answer









    $endgroup$


















      4












      $begingroup$

      Let $s$ for which $Re(s)>1$ then, for all $p in mathbb{P}$ we have $$sum_{k=1}^{infty} frac{1}{p^{ks}}=left(1-frac{1}{p^s}right)^{-1}$$



      Now let $A(N)$ be the set of all strictly positive numbers such as all prime divisors are at maximum $N$.



      Then $$prod_{p in mathbb{P},text{ }p<N}left(1-frac{1}{p^s}right)^{-1}=sum_{n in A(N)}frac{1}{n^s}$$



      Obviously ${1,...,N}subset A(N)$, then



      $$left|zeta(s)-prod_{p in mathbb{P},text{ }p<N}left(1-frac{1}{p^s}right)^{-1}right|le sum_{n>N}frac{1}{n^{Re{(s)}}}$$



      When $N$ goes to infinity it gives the result.






      share|cite|improve this answer









      $endgroup$
















        4












        4








        4





        $begingroup$

        Let $s$ for which $Re(s)>1$ then, for all $p in mathbb{P}$ we have $$sum_{k=1}^{infty} frac{1}{p^{ks}}=left(1-frac{1}{p^s}right)^{-1}$$



        Now let $A(N)$ be the set of all strictly positive numbers such as all prime divisors are at maximum $N$.



        Then $$prod_{p in mathbb{P},text{ }p<N}left(1-frac{1}{p^s}right)^{-1}=sum_{n in A(N)}frac{1}{n^s}$$



        Obviously ${1,...,N}subset A(N)$, then



        $$left|zeta(s)-prod_{p in mathbb{P},text{ }p<N}left(1-frac{1}{p^s}right)^{-1}right|le sum_{n>N}frac{1}{n^{Re{(s)}}}$$



        When $N$ goes to infinity it gives the result.






        share|cite|improve this answer









        $endgroup$



        Let $s$ for which $Re(s)>1$ then, for all $p in mathbb{P}$ we have $$sum_{k=1}^{infty} frac{1}{p^{ks}}=left(1-frac{1}{p^s}right)^{-1}$$



        Now let $A(N)$ be the set of all strictly positive numbers such as all prime divisors are at maximum $N$.



        Then $$prod_{p in mathbb{P},text{ }p<N}left(1-frac{1}{p^s}right)^{-1}=sum_{n in A(N)}frac{1}{n^s}$$



        Obviously ${1,...,N}subset A(N)$, then



        $$left|zeta(s)-prod_{p in mathbb{P},text{ }p<N}left(1-frac{1}{p^s}right)^{-1}right|le sum_{n>N}frac{1}{n^{Re{(s)}}}$$



        When $N$ goes to infinity it gives the result.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Dec 12 '15 at 18:16









        Hexacoordinate-CHexacoordinate-C

        730829




        730829






























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