Math nerds love to take any opportunity to celebrate the mathematical beauty of a date. The way we keep track of days is a human-made system that has no bearing on the way the universe works, but we've done it for a long time and we may as well have fun with it. We observe Pi Day in March (3/14) and Square Root Day occasionally (3/3/09, 4/4/16 and 5/5/25). But today is also "a date of mathematical beauty."
Written as 9/16/25 (as Americans do), today's date consists of three perfect squares. There won't be another date that does this until the next century. Mathematician Colin Adams points out that those particular squares are special because they are a Pythagorean triple, which illustrates the Pythagorean theorem: the square of the hypotenuse is equal to the sum of the squares of the other two sides. Adams explains how that happens on 9/16/25 at NPR.
While we normally celebrate Pi Day by eating pie, Adams is celebrating Pythagorean Triple Square Day with the precisely-cut cakes shown above. We should all use this date as an excuse to eat cake, too. -via Damn Interesting
(Image credit: Colin Adams)