Thread: Proof of integers

Let a,b and n be positive integers with n ≥ 2. Prove that:

gcd((n^a) - 1, (n^b) - 1)= n^(gcd(a,b)) - 1.

Help please!! I have no idea how to do this!

A starting point might be similar to:

so if n = dk, with d = gcd(n,m)

and the same for m = dq