happy number

English

Etymology

Popularised by the British mathematician Reginald Allenby in the 1960s, who developed this concept from his daughter, while similar mathematical formulas may have existed earlier in Russia. The number was called "happy" because the iteration to reach 1 was treated like a game of numbers, where reaching 1 is compared to "winning" that game.

Noun

happy number (plural happy numbers)

  1. (mathematics) Any number that eventually reaches 1 after some number of iterations of replacing each of its digits by the sum of that digit's squares.
    Antonyms: sad number, unhappy number
    13 is a happy number because 1² + 3² is 10, and 1² + 0² is 1.
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