N is a positive integer such that each of 3*N + 1 and 4*N + 1 is a perfect square.
Is N always divisible by 56?
If so, prove it. Otherwise, give a counterexample.
(In reply to A start
Try mod7. a must be either 0 mod 7 or +/-3 mod7.
I did , advanced a little, but still did not prove the thing.
Maybe you will...