"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 equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1."

This description makes people think think that the numbers that "loop endlessly in a cycle which does not include 1" are also happy numbers.

The part "or it loops endlessly in a cycle which does not include 1" should be put in another sentence saying that: unhappy numbers should be like: XXXX.