Kaprekar number

In mathematics, a natural number in a given number base is a ${\displaystyle p}$-Kaprekar number if the representation of its square in that base can be split into two parts, where the second part has ${\displaystyle p}$ digits, that add up to the original number. For example, in base 10, 45 is a 2-Kaprekar number, because 45² = 2025, and 20 + 25 = 45. The numbers are named after D. R. Kaprekar.