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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).

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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