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Search: id:A056069
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| A056069 |
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Number of 4-element ordered antichains on an unlabeled n-element set; T_1-hypergraphs with 4 labeled nodes and n hyperedges. |
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+0
4
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| 25, 454, 3818, 21420, 92805, 335152, 1055944, 2990020, 7767357, 18789070, 42797602, 92588216, 191542842, 381000192, 731941256, 1363109096, 2468549141
(list; graph; listen)
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OFFSET
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4,1
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COMMENT
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T_1-hypergraph is a hypergraph (not necessarily without empty hyperedges or multiple hyperedges) which for every ordered pair of distinct nodes has a hyperedge containing one but not the other node.
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REFERENCES
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V. Jovovic and G. Kilibarda, On the number of Boolean functions in the Post classes F^{mu}_8, Diskretnaya Matematika, 11 (1999), no. 4, 127-138 (translated in Discrete Mathematics and Applications, 9, (1999), no. 6)
V. Jovovic, G. Kilibarda, On enumeration of the class of all monotone Boolean functions, in preparation.
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LINKS
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K. S. Brown, Dedekind's problem
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FORMULA
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a(n)=C(n + 15, 15) - 12*C(n + 11, 11) + 24*C(n + 9, 9) + 4*C(n + 8, 8) - 18*C(n + 7, 7) + 6*C(n + 6, 6) - 36*C(n + 5, 5) + 36*C(n + 4, 4) + 11*C(n + 3, 3) - 22*C(n + 2, 2) + 6*C(n + 1, 1).
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CROSSREFS
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Cf. A051112 for 4-element (unordered) antichains on a labeled n-element set, A056005.
Sequence in context: A016633 A001811 A131279 this_sequence A089386 A014927 A059946
Adjacent sequences: A056066 A056067 A056068 this_sequence A056070 A056071 A056072
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KEYWORD
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nonn
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AUTHOR
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Vladeta Jovovic, Goran Kilibarda (vladeta(AT)Eunet.yu), Jul 26 2000
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