Happy number
A kind of number
About Happy number
A happy number is a number which, when you replace it by the sum of the squares of its digits and repeat, eventually reaches 1. Numbers that do not reach 1 enter the cycle 4, 16, 37, 58, 89, 145, 42, 20, 4 and are unhappy.
Key features
- 1, 7, 10, 13, 19, 23, 28, 31, … are happy.
- All numbers in the cycle above are unhappy.
Examples:
1, 7, 10, 13, 19, 23, 28, 31, 32, 44, 49, 68, 70