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Search: id:A055533
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| A055533 |
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Number of labeled order relations on n nodes in which longest chain has n-1 nodes. |
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+0
6
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| 1, 12, 108, 960, 9000, 90720, 987840, 11612160, 146966400, 1995840000, 28979596800, 448345497600, 7366565606400, 128152088064000, 2353813862400000, 45527990796288000, 925143000477696000
(list; graph; listen)
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OFFSET
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2,2
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COMMENT
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Also number of labeled acyclic digraphs with n nodes and binomial(n,2)-1 arcs, cf. A081064. - Vladeta Jovovic (vladeta(AT)eunet.rs), Jul 14 2008
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REFERENCES
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L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 60.
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FORMULA
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E.g.f.: (x^2/2)(1+x)/(1-x)^3. a(n)=n!(n-1)^2/2, if n>1. - Vladeta Jovovic (vladeta(AT)eunet.rs), Dec 01 2002
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PROGRAM
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(PARI) a(n)=if(n<2, 0, n!/2*(n-1)^2) - Michael Somos Mar 06 2004
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CROSSREFS
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A column or diagonal of triangle in A008285.
Sequence in context: A037972 A111990 A053469 this_sequence A037602 A037707 A140317
Adjacent sequences: A055530 A055531 A055532 this_sequence A055534 A055535 A055536
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), Jul 10 2000
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EXTENSIONS
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More terms from Vladeta Jovovic (vladeta(AT)eunet.rs), Dec 01 2002
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