TITLE: prove that there are infinitely many integers n so that 3 does not divide $\phi(n)$
QUESTION [6 upvotes]: prove that there are infinitely many integers n so that 3 does not divide $\phi(n)$
I began to look at the problem with the residue classes of 3. I am not sure if this is correct.

REPLY [2 votes]: referring to this answer, consider the numbers of the form $2^k, 5^k,11^k$ as well.