There is an interesting property for the sum of first N odd numbers. For example sum of first 3 odd numbers, 1 + 3 + 5 = 9 which is 3². Take another example: sum of first 5 odd numbers, 1 + 3 + 5 + 7 + 9 = 25 which is 5².

This means that sum of first N odd numbers is N².

Any proof?. Of course there are algebraic proofs. But we are considering a geometric proof.