Type: Article

On a variation of a congruence of subbarao

Dujella, Andrej; Luca, Florian;

Abstract:

We study positive integers n such that n phi(n) equivalent to 2 mod sigma(n), where phi(n) and sigma(n) are the Euler function and the sum of divisors function of the positive integer n, respectively. We give a general ineffective result showing that there are only finitely many such n whose prime factors belong to a fixed finite set. When this finite set consists only of the two primes 2 and 3 we use continued fractions to find all such positive integers n.