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There are 23 known natural numbers n such that 2n does not contain the digit 2. Their sum ends with 23, which is one of them. The prime cases are easy to remember: 2, 3, 23 and ... the 23th prime! [Capelle]

 

  Submitted: 2009-06-10 10:06:38;   Last Modified: 2011-02-20 12:33:07.



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