Someone just wanted to make a grid of squares animate in diagonally. This takes a series of numbers and maps them to rows and columns using triangular numbers. (It might’ve been more straightforward to just invert the Cantor pairing function.)
I added little fractions text, so it doubles as a visual proof of the countability of the rationals! And then I made two, so it doubles as a visual proof of the fact that the sum of consecutive triangular numbers is a square number!
Refresh for a different pair of consecutive triangle numbers.
See also: