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Lucky Numbers (Posted on 2005-02-19) Difficulty: 4 of 5
Call an integer lucky if it is a sum of positive integers (not necessarily distinct) whose reciprocals sum to 1. For example, 4 and 11 are lucky: 4=2+2 and 1/2+1/2=1, and 11=2+3+6 and 1/2+1/3+1/6=1. But 2, 3, and 5 are unlucky. How many unlucky positive integers are there?

See The Solution Submitted by David Shin    
Rating: 3.7500 (4 votes)

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Answer | Comment 4 of 5 |
There are precisely 13 unlucky positive integers.
  Posted by K Sengupta on 2008-03-21 14:58:52
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