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A004121 Generalized weak orders on n points.
(Formerly M2095)
+0
4
2, 16, 208, 3968, 109568, 4793344, 410662912, 82657083392, 38274970222592, 37590755515826176, 75458309991776124928, 305873605165090925969408, 2491832958314452159507202048, 40704585435508852018947014262784 (list; graph; listen)
OFFSET

1,1

REFERENCES

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.

FORMULA

E.g.f.: 1/(1-Sum_{i >= 1} 2^binomial(i+1, 2)*x^i/i!).

CROSSREFS

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

KEYWORD

nonn,nice,easy

AUTHOR

njas

EXTENSIONS

Formula and more terms from Vladeta Jovovic (vladeta(AT)Eunet.yu), Mar 27 2001

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Last modified July 24 12:00 EDT 2008. Contains 142294 sequences.


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