Art of Problem Solving

Dirichlet's Theorem: Difference between revisions

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==Stronger Result==
==Stronger Result==
For any positive integers <math>a</math> and <math>m</math> such that <math>(a,m)=1</math>,  
For any positive integers <math>a</math> and <math>m</math> such that <math>\gcd(a,m)=1</math>,  
<cmath>
<cmath>
\sum_{\substack{p\leq x\\ p\equiv a\mod m}}\frac{1}{p}=\frac{1}{\phi(m)}\log\log x+O(1)
\sum_{\substack{p\leq x\\ p\equiv a\mod m}}\frac{1}{p}=\frac{1}{\phi(m)}\log\log x+O(1)

Latest revision as of 10:22, 3 February 2025

Theorem

For any positive integers $a$ and $m$ such that $\gcd(a,m)=1$, there exists infinitely many prime $p$ such that $p\equiv a\mod m$

Hence, for any arithmetic progression, unless it obviously contains finitely many primes (first term and common difference not coprime), it contains infinitely many primes.

Stronger Result

For any positive integers $a$ and $m$ such that $\gcd(a,m)=1$, \[\sum_{\substack{p\leq x\\ p\equiv a\mod m}}\frac{1}{p}=\frac{1}{\phi(m)}\log\log x+O(1)\] where the sum is over all primes $p$ less than $x$ that are congruent to $a$ mod $m$, and $\phi(x)$ is the totient function.

See Also