Which condition is sufficient for gcd(an−1,am−1)=agcd(n,m)−1\text{gcd}(a^n-1, a^m-1) = a^{\text{gcd}(n, m)} - 1gcd(an−1,am−1)=agcd(n,m)−1?
a>1,n,m∈Z+a > 1, n, m \in \mathbb{Z}^+a>1,n,m∈Z+
a=1a = 1a=1
a<0a < 0a<0
It is never true