# Happy Primes

A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number either equals 1 (where it will stay), or it loops endlessly in a cycle that does not include 1. Those numbers for which this process ends in 1 are happy numbers, while those that do not end in 1 are unhappy numbers (or sad numbers).

More formally, given a number n=n_{0}, define a sequence n_{1}, n_{2}, ... where n_{i+1} is the sum of the squares of the digits of n_{i}. Then n is happy if and only if there exists i such that n_{i}=1.

If a number is happy, then all members of its sequence are happy; if a number is unhappy, all members of the sequence are unhappy.

For example, 19 is happy, as the associated sequence is:

- 1
^{2}+ 9^{2}= 82 - 8
^{2}+ 2^{2}= 68 - 6
^{2}+ 8^{2}= 100 - 1
^{2}+ 0^{2}+ 0^{2}= 1.

First 20: 7, 13, 19, 23, 31, 79, 97, 103, 109, 139, 167, 193, 239, 263, 293, 313, 331, 367, 379, 383

Checkout list of first: 10, 50, 100, 500, 1000 happy primes. You can also check all happy primes.

## External#

- OEIS: A035497
- Wikipedia: Happy Numbers

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