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Easy count (Posted on 2014-07-29) Difficulty: 3 of 5
Let S be a set of some positive integers.
We'll call S autonomous if the number of elements in S is itself an element of S. e.g. the set {2,3,5} is autonomous, as is the set {2,7}, but the sets {1, 4} or {2,4,5} are not.

Determine a general formula for the number
of autonomous subsets of {1, 2, 3, ... , n}.

See The Solution Submitted by Ady TZIDON    
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  Subject Author Date
re(2): SolutionAdy TZIDON2014-07-30 17:00:49
re: SolutionCharlie2014-07-30 09:57:26
SolutionSolutiontomarken2014-07-30 08:48:04
Hints/Tipsre: computer assisted solutionAdy TZIDON2014-07-29 23:53:21
Solutioncomputer assisted solutionCharlie2014-07-29 14:38:40
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