Since any positive integer n is of the form 2p or, 2p + 1
When n = 2p,
then n2 = 4p2 = 4a
where a = p2
When n = 2p + 1,
then n2 = (2p + 1)2 = 4p2 + 4p + 1
⇒ 4p(p + 1) + 1 ⇒ 4m + 1
where m = p(p + 1)
Therefore square of any positive integer is of the form 4q or 4q + 1 for some integer q