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A note on primes in certain residue classes

Abstract

Given positive integers a1,. .. , a k , we prove that the set of primes p such that p ≡ 1 mod ai for i = 1,. .. , k admits asymptotic density relative to the set of all primes which is at least k i=1 1 − 1 ϕ(a i) , where ϕ is the Euler's totient function. This result is similar to the one of Heilbronn and Rohrbach, which says that the set of positive integer n such that n ≡ 0 mod ai for i = 1,. .. , k admits asymptotic density which is at least k i=1