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Search: id:A004121
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| A004121 |
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Generalized weak orders on n points.
(Formerly M2095)
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+0
4
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| 2, 16, 208, 3968, 109568, 4793344, 410662912, 82657083392, 38274970222592, 37590755515826176, 75458309991776124928, 305873605165090925969408, 2491832958314452159507202048, 40704585435508852018947014262784
(list; graph; listen)
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OFFSET
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1,1
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
I. P. Goulden and D. M. Jackson, Combinatorial Enumeration, John Wiley and Sons, N.Y., 1983.
C. G. Wagner, Enumeration of generalized weak orders. Arch. Math. (Basel) 39 (1982), no. 2, 147-152.
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FORMULA
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E.g.f.: 1/(1-Sum_{i >= 1} 2^binomial(i+1, 2)*x^i/i!).
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CROSSREFS
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Cf. A004122, A004123, A000670 (asymmetric generalized weak orders on n points)
Adjacent sequences: A004118 A004119 A004120 this_sequence A004122 A004123 A004124
Sequence in context: A161568 A138429 A087923 this_sequence A114531 A012056 A062971
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KEYWORD
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nonn,nice,easy
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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Formula and more terms from Vladeta Jovovic (vladeta(AT)eunet.rs), Mar 27 2001
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