Q: Let p and q be prime numbers. Prove that pq + 1 is a square if and only if p and q are twin primes.
(<=)
Pf: p and q are twin primes (i.e. - p = q+2)
Therefore, pq+1 = q(q+2) +1 = q^2 + 2*q +1 = (q+1)^2
(=>)
This is where I'm stuck.
Pf: (By Contradiction?)
What is a way to show that p and q are not twin primes?
Is it something like p-q > 2?
How would I use something like that to form a contradiction?