This came up during tutoring. Alexander learned what a perfect number is, a positive integer equal to the sum of its divisors (including one and excluding itself). Six is a perfect number: 6 = 1+2+3. Twenty-eight is a perfect number: 28 = 1+2+4+7+14.

Then we learned that all

**even**perfect numbers are triangular numbers. That is when Alexander reminded me, no, chastised me, about Pascal's triangle. Which boy forgets nothing?

artwork courtesy of Wikipedia and David Tung on Quora