From: Hans Fugal <fugalh@...>
Date: 2006-09-02T07:20:34+09:00
Subject: Re: Happy Numbers (#93)

Phrogz wrote:
> 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.
> 

This isn't a math quiz. It's a programming quiz.