Pi Day (March 14) is a day of global mathematical celebration, but it’s not the only numerically significant calendar date. Not only is each number in today’s date (9/16/25) a perfect square—their consecutive square roots are also an example of a Pythagorean triple. While an official name has yet to be assigned, “Pythagorean Triple Square Day” encapsulates the moment pretty perfectly. But regardless of authorship, the Pythagorean Theorem helped revolutionize modern concepts in math, geometry, architecture, music, and numerous other fields. The next Pythagorean Triple Square Day won’t take place for quite some time.