This could be helpfullhelpful: "Certain other cases of Dirichlet's Theorem have been proved by elementary methods;inmethods; in fact,elementary elementary proofs have been found for general classes..classes…. M. Brauer found a rather simple proof that there are infinitely many primes of the form $ak+1$ and $ak-1$ for every positive integer a"$a$".Topics in the theory of numbers Topics in the theory of numbers by Paul ErdosErdős and Janos Suranyi page 178-180pages 178–180.