What happened 2 days ago?

Two days ago was September 16, 2025. 

Unless you are a mathematician, chances are you were not aware of the special character of that day. I, myself, heard on NPR that very day was a mathematically rare gem—a once-in-a-century date known as Pythagorean Triple Square Day. 

Here’s why it’s special, each number in the date was a perfect square: 9 = 3², 16 = 4² and 25 = 5² 9 = 3², 16 = 4² and 25 = 5² Those square roots—3, 4, and 5—form a Pythagorean triple, meaning: 3² + 4² + 5² or 9 + 16 + 25 

This aligns with the Pythagorean Theorem: a² + b² = c² That describes the relationship between the sides of a right triangle. What makes this date even more poetic, is that it’s the only date in the 21st century where all three components are perfect squares from a Pythagorean triple. 

Even the year—2025—is a perfect square: 45² Some math lovers celebrated with rectangular cakes sliced diagonally into right triangles, inscribed with the date in icing. A sweet tribute to hidden harmony. Just try to walk back into time (it's only 2 days, no one will ever know) as if you were there when that happened, especially since it won’t happen again for another century!