Consider the sequence an=2n+1a_n = 2^{n} + 1an=2n+1. For which nnn is gcd(an,an+1)=1\text{gcd}(a_n, a_{n+1}) = 1gcd(an,an+1)=1?
No nnn
Only n=1n=1n=1
All odd nnn
All even nnn