Does this recursion problem have a typo?

Question

Just wondering how to cast this sentence into the actual intention — #8

Answer 1

The notation $(a_n,a_{n+1})=1$ can mean that the greatest common divisor of $a_n$ and $a_{n+1}$ is $1$;

i.e., $a_n$ and $a_{n+1}$ are relatively prime.

Answer 2

No it does not. This is common notation for greatest common divisor. That is, $(a,b) = 1$ means that $a$ and $b$ only share $1$ as a divisor.