Yes, this is most definitely the sum of 100 to 1. The best way to see this w/o paper and a calculator is to consider that 100^2 - 99^2 is really (100 + 99) (100 - 99) = 199 and 2^2 - 1^2 is really (2 + 1)(2-1) = 3. The lower squares mirror their higher counterparts such that you get 25 pairs that equal 202. 202*25 = 5050.