Overview
- Written as 9/16/25, the month, day, and year are 9, 16, and 25—each a perfect square whose roots 3, 4, and 5 form a Pythagorean triple.
- Outlets report this is the only date in the 21st century whose consecutive square roots satisfy 3² + 4² = 5².
- Coverage adopts the informal name “Pythagorean Triple Square Day,” with no official designation announced.
- Mathematicians emphasized the outreach value, with Williams College’s Colin Adams celebrating with a right-triangle cake and CUNY’s Terrence Blackman praising the date’s “mathematical poetry.”
- The quirk depends on the U.S. month/day/year format, and the year 2025 is itself a perfect square (45 × 45).