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A246537
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The number of collections F of subsets of {1,2,...,n} such that the union of F is not an element of F.
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2
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1, 1, 3, 97, 32199, 2147318437, 9223372023969379707, 170141183460469231667123699412802366921, 57896044618658097711785492504343953925273862865136528165617039157077296866063
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OFFSET
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0,3
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COMMENTS
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Equivalently, the number of partial orders (on some subset of the powerset of {1,2,...,n} ordered by set inclusion) that contain no maximal elements (the empty family) or at least two maximal elements.
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LINKS
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FORMULA
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a(n) = 2^(2^n) - Sum_{k=0..n} C(n,k)*2^(2^k-1).
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EXAMPLE
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a(2) = 3 because we have: {}, {{1},{2}}, {{},{1},{2}}.
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MATHEMATICA
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Table[2^(2^n) - Sum[Binomial[n, k] 2^(2^k - 1), {k, 0, n}], {n, 0,
10}]
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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