Divisibility of prime numbers
Hint
By Euclid's lemma we have: if $p$ is prime then $$p|ab\Rightarrow p|a\lor p|b$$
Now write $a^n=a\times a^{n-1}$ and use a descending induction.
Divisibility of prime numbers
Hint
By Euclid's lemma we have: if $p$ is prime then $$p|ab\Rightarrow p|a\lor p|b$$
Now write $a^n=a\times a^{n-1}$ and use a descending induction.