Give reason to show that none of the numbers 640, 81000 and 3600000 is a perfect square.

Evaluate:

37² - 36²

Evaluate:

101² - 100²

Without doing the actual addition, find the sum of:

1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19 + 21 + 23