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The only odd untouchable (Posted on 2016-04-12) Difficulty: 3 of 5
An untouchable number is a positive integer that is not the sum of the proper divisors of any number(see OEIS A005114).

It is thought that 5 is the only odd untouchable number.


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  Subject Author Date
SolutionGoldbach SolutionBrian Smith2016-04-12 12:37:55
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