1. ## proving congruences

I am having trouble with proving this particular congruence.

n^21 is congruent to n(mod 30)

2. Originally Posted by meshel88
I am having trouble with proving this particular congruence.

n^21 is congruent to n(mod 30)
What have you tried?

3. I know that I have to prove that 2,3,5 divide n^21-n but that is where I get stuck.