# 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!