From: Phrogz <gavin@...>
Date: 2006-09-02T06:30:40+09:00
Subject: Re: Happy Numbers (#93)

Hans Fugal wrote:
> And what the quiz neglected to mention is that there is an easy test for
> unhappy number, which the mathworld page enumerates:
>
> 	Iterating this sum-of-squared-digits map always eventually
> 	reaches one of the 10 numbers 0, 1, 4, 16, 20, 37, 42, 58, 89,
> 	or 145 (Sloane's A039943; Porges 1945).
>
> So if you hit one of those unhappy numbers you know you're in an unhappy
> loop.

IMO, that's an unnecessary spoiler (which is why I didn't look at the
Wolfram page). You can figure it out on your own without a 'cheat
sheet' of numbers.