Happy numbers

Topics:easy math

Happy numbers are positive integers that follow a particular formula: take each individual digit, square it, and then sum the squares to get a new number. Repeat with the new number and eventually, you might get to a number whose squared sum is 1. This is a happy number. An unhappy number (or sad number) is one that loops endlessly. Write a function that determines if a number is happy or not.
test not run
(= (__ 7) true)
test not run
(= (__ 986543210) true)
test not run
(= (__ 2) false)
test not run
(= (__ 3) false)

Code which fills in the blank: