CSS animation demo of the derivation of the sum of natural numbers.

S = 1 + 2 + 3 + ... + (n - 2) + (n - 1) + n + S = 1 + 2 + 3 + ... + (n - 2) + (n - 1) + n 2 S = (n + 1) 1 2 3 (n-3) (n-2) (n-1) n