From The Archives: 381654729

Originally published on September 17, 2011, 6:21 pm.

You might wonder why I’m focusing on a single number. Well, during last year’s exams, my registration number was 381654729 — a seemingly random 9-digit number. Like most people, I didn’t pay much attention to it and soon forgot about it after the results came out. But this morning, something incredible happened. While flipping through the October 2010 issue of Mathematics Today (page 8), I was in for a surprise: my old registration number wasn’t just any number — it was extraordinary.

381654729 is a nine-digit number where each digit from 1 to 9 appears exactly once. More astonishingly, it’s divisible by 9. But the magic doesn’t stop there. If you remove the last digit, the remaining eight digits form a number divisible by 8. Remove another digit, and the resulting seven-digit number is divisible by 7. This remarkable pattern continues all the way down to a single digit.

As it turns out, this type of number has a name: it’s called a “polydivisible number.”

Mathematics truly has a way of revealing wonders — often when you least expect it!