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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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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)
Sequence in context: A036081 A138429 A087923 this_sequence A114531 A012056 A062971
Adjacent sequences: A004118 A004119 A004120 this_sequence A004122 A004123 A004124
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KEYWORD
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nonn,nice,easy
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AUTHOR
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njas
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EXTENSIONS
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Formula and more terms from Vladeta Jovovic (vladeta(AT)Eunet.yu), Mar 27 2001
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