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Search: id:A092880
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| A092880 |
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Number of ordered 2-multiantichains on an n-set. |
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+0
5
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| 1, 2, 6, 26, 126, 602, 2766, 12266, 52926, 223802, 932526, 3844106, 15722526, 63936602, 258902286, 1045109546, 4209004926, 16921851002, 67945160046, 272554432586, 1092540156126, 4377129999002, 17529432313806, 70180474597226
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OFFSET
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0,2
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COMMENT
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Let P(A) be the power set of an n-element set A and R be a relation on P(A) such that for all x, y of P(A), xRy if either 0) x is not a subset of y and y is not a subset of x, or 1) x equals y. Then a(n) = |R|. [From Ross La Haye (rlahaye(AT)new.rr.com), Mar 19 2009]
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REFERENCES
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Ross La Haye, Binary Relations on the Power Set of an n-Element Set, Journal of Integer Sequences, Vol. 12 (2009), Article 09.2.6. [From Ross La Haye (rlahaye(AT)new.rr.com), Mar 19 2009]
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FORMULA
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a(n) = 4^n-2*3^n+2*2^n.
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CROSSREFS
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Cf. A092881-A092884.
Sequence in context: A027239 A050890 A114710 this_sequence A034474 A123872 A030937
Adjacent sequences: A092877 A092878 A092879 this_sequence A092881 A092882 A092883
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KEYWORD
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nonn
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AUTHOR
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Goran Kilibarda, Vladeta Jovovic (vladeta(AT)eunet.rs), Mar 10 2004
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