What's especially fascinating is that the core of the problem is a generalization of the totient computation, so understanding the inclusion-exclusion construction of totient is very helpful to the problem, while simply memorizing the formula is a misdirection.
OP missing this point shows that he really was doing this for all the wrong reasons. He should have done FIRST or science bowl instead.
OP missing this point shows that he really was doing this for all the wrong reasons. He should have done FIRST or science bowl instead.