Consider a series of numbers, defined as follows:

Starting with any natural number, each member is a sum of the squares of the previous member`s digits.

Prove : The series always reaches either a stuck-on-one sequence: 1,1,1… or a closed loop of the following 8 numbers: 145,42,20,4,16,37,58,89, ...

Ex1: 12345,55,50,25,29,85,89,145….. etc

Ex2: 66,72,53,34,25,29,85,89,145…

Ex3: 91,10,1,1,1…..