Simon has created a Python program that looks for “squangular” numbers.
36 is both a square number (6×6 square of things makes 36 things) and a triangular number (8×8 triangle of things makes 36 things). I call this kind of numbers squangular. Squangular numbers are both square and triangular.
Squangular numbers are rare, like the next squangular number is 1225. The next one is 41616, then 1413271, then 48024900, and after that I didn’t bother checking.
Link to code here: https://repl.it/@simontiger/SquangularNumbers#main.py