I think you are expected to know that if then , where phi is the Euler phi function
I suspect you are capable of sussing things out from there.
Define a sequence by and for . Which integers between and inclusive occur as the last two digits in the decimal expansion of infinitely many .
It would take a long time to do this by brute force. What exactly does this mean (this was a hint that was given)?: If does not divide , then is determined by . So for example, is determined by .