Today's date, October 24, 2026, marks the last Pythagorean Theorem Day of the 21st century. Written in the month-day-year format as 10/24/26, its numbers form a Pythagorean triple, as 10² + 24² = 26² (100 + 576 = 676). Such dates satisfy the mathematical rule for right-angled triangles. The next Pythagorean Theorem Day will occur again on March 4, 2105.