Eladio Torres

Today, the calendar makes a right triangle, for the last time this century. This Saturday is October 24, 2026. Write it as 10/24/26 or 24/10/26, and the same beautiful relationship appears: 10² + 24² = 26² 100 + 576 = 676 But here’s what makes today special. There are infinitely many Pythagorean triples. Only a handful fit our calendar. Using the rule month² + day² = (last two digits of the year)², the month cannot exceed 12, and the day cannot exceed 31. Those small limits leave exactly 12 qualifying dates in this century. Today is the last. The next will be March 4, 2105: 3² + 4² = 5² That is a wait of more than 78 years. An infinite family of triangles. Just twelve appearances on a century’s calendar. Happy Pythagorean Triple Day.

At age 12, Edward Nelson began experimenting with a deck of cards, repeatedly rearranging it top-bottom, top-bottom. He asked a simple question: after how many repetitions will the deck return to its original order? He generalized the problem to decks of different sizes, plotted the results, found a formula by age 14, and proved it a year later. A nice example of how serious mathematics can begin with nothing more than curiosity and a deck of cards. Source: Mathematicians: An Outer View of the Inner World, Edward Nelson.