Happy number
NUMBERS WITH A CERTAIN PROPERTY INVOLVING RECURSIVE SUMMATION
Happy Numbers; Unhappy number; Happy Number; Unhappy Numbers; Happy prime; Sad Numbers; Happy numbers; Sad number; Happy prime number
In number theory, a happy number is a number which eventually reaches 1 when replaced by the sum of the square of each digit. For instance, 13 is a happy number because 1^2+3^2=10, and 1^2+0^2=1.