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|Two happy ends (Posted on 2011-03-07)
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
| Comment 1 of 11
The in-my-head D1 part at least.
No 3 (or more) digit number can ever be followed by a larger term. This means if the starting number has more than 3 digits, some successive term will have fewer than 3 digits.
If you then continue finding terms there must eventually be a repeat and you have a cycle.
I suppose this doesn't prove you get one of the two cycles given in the problem. I suppose if I had the patience to check where all the numbers 1 to 99 go that would count as D2.
Posted by Jer
on 2011-03-07 14:32:20
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