(In reply to

Mod 4 by Ady TZIDON)

Ady:

I'd be interested in your Mod 4 proof, since I couldn't make that work, and I have doubts that it does work.

b^2-4*a*c = 1 (mod 4), so it looks like it could conceivably be a square.

Plus, 4ac = 0 (mod 4), even if a or c are even, which is another reason I doubt it will work.

But I'd like to be proved wrong,

Steve