The Kaprekar number reference article from the English Wikipedia on 24-Apr-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Kaprekar number

A Kaprekar number is a number that, in a given base, the digits of its square can be split off into two numbers with as many digits as the original number, and these two new numbers add up to the original number.

For example, the 3-digit number 703 squared is 494209. We split 494209 into two new 3-digit numbers, 494 and 209, and we find that 494 + 209 = 703.

The first few Kaprekar numbers are

1, 9, 45, 55, 99, 297, 703

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