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A320726
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Composite numbers such that all other numbers obtained from all permutations of all subsets of the digits are noncomposite.
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1
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4, 6, 8, 9, 10, 20, 22, 30, 32, 33, 35, 50, 55, 70, 77, 111
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OFFSET
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1,1
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COMMENTS
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Sequence is finite since it is a subsequence of a finite sequence (A071070).
This is complete: there are only 16 terms in the sequence.
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LINKS
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EXAMPLE
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371 is in this sequence because it's composite and none of the numbers 1, 3, 7, 13, 17, 31, 37, 137, 173, 317, 713 and 731 is composite.
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MATHEMATICA
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Select[Range[4, 10^3], Function[n, And[CompositeQ@ n, NoneTrue[DeleteCases[Flatten@ Map[If[Length@ # > 1, FromDigits /@ Permutations@ #, #] &, Rest@ Subsets@ IntegerDigits@ n], _?(# == n &)], CompositeQ]]]] (* Michael De Vlieger, Nov 13 2018 *)
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CROSSREFS
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KEYWORD
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nonn,base,fini,full
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AUTHOR
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STATUS
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approved
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