Interesting math for numbers 0 to 9999

Erich Friedman, an associate professor of mathematics at Stetson University in Florida, has this page “What’s Special About This Number?“. Though he doesn’t cover every number, he has some interesting math for 2849 of them. If you know something interesting about numbers he hasn’t covered let him know. Here’s a few:

  • 16 is the only number of the form xy = yx with x and y different integers.
  • 4349 is the largest known number n so that 46n – 45n is prime.
  • 4624 = 44 + 46 + 42 + 44.
  • 6327 = 324 + 325 + . . . + 342 = 343 + 344 + . . . + 360.

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