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Search: id:A053554
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| A053554 |
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Labled series-parallel posets with n points. |
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+0
4
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| 1, 3, 19, 195, 2791, 51303, 1152019, 30564075, 935494831, 32447734143, 1257770533339, 53884306900515, 2528224238464471, 128934398091500823, 7101273378743303779, 420078397130637237915, 26563302733186339752511
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Labeled N-free posets. - Detlef Pauly (dettodet(AT)yahoo.de), Dec 27 2002
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REFERENCES
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R. P. Stanley, Enumeration of posets generated by disjoint unions and ordinal sums. Proc. Amer. Math. Soc. 45 (1974), 295-299
R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.39.
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LINKS
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Index entries for reversions of series
Index entries for sequences related to posets
S. R. Finch, Series-parallel networks
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FORMULA
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E.g.f. is reversion of ln(1+x)-x^2/(1+x).
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MAPLE
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read format; read transforms; f1 := ln(1+x)-x^2/(1+x); f2 := series(f1/x, x, 30); EGF053554 := seriestoseries(f2, 'revogf'); A053554 := n->n!*coeff(EGF053554, x, n);
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CROSSREFS
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Cf. A000112 (unlabeled posets), A001035 (labeled posets), A003430 for the unlabeled analogue of A053554.
A053554(n) = A058349(n) + A058350(n) (n>=2).
Sequence in context: A028854 A108292 A048172 this_sequence A079145 A000763 A001832
Adjacent sequences: A053551 A053552 A053553 this_sequence A053555 A053556 A053557
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KEYWORD
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nonn,easy,nice
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), Jan 16 2000
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