Primes on the form $p^2-1$ Prove that there exists a unique prime number of the form $p^2 − 1$ where $p\geq 2$ is an integer.
I have no idea how to approach the question. any hints will be greatly appreciated

$n(x) = n^2-1$
$n(x) = n^2-1^2$
$n(x) = (n+1)(n-1)$
For it to be prime it has to be only be divisible by itself. What to do from here?
