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Eliot Ness meets Paul Erdős (Posted on 2015-01-23) Difficulty: 2 of 5
An untouchable number is a positive integer that cannot be expressed as the sum of all the proper divisors of any positive integer (including the untouchable number itself).

Prove:
i. There is no untouchable number that is one more than a prime.
ii. Except number 5, there is no untouchable number that is
three more than a prime.

No Solution Yet Submitted by Ady TZIDON    
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  Subject Author Date
re(2): SolutionSteve Herman2015-01-26 08:51:40
re: SolutionKenny M2015-01-25 17:24:57
SolutionSolutionJer2015-01-23 08:11:40
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