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A020558
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Number of ordered multigraphs on n labeled edges (without loops).
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2
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1, 1, 4, 27, 274, 3874, 71995, 1682448, 47840813, 1615315141, 63566760077, 2873099980637, 147384910116793, 8496500896980637, 545845612016485842, 38797966029876716897, 3032005571734589578076
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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REFERENCES
| G. Labelle, Counting enriched multigraphs..., Discrete Math., 217 (2000), 237-248.
G. Paquin, D\'enombrement de multigraphes enrichis, M\'emoire, Math. Dept., Univ. Qu\'ebec \`a Montr\'eal, 2004.
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FORMULA
| E.g.f.: exp((3*x-2)/(2-2*x))*Sum(1/(n!*(1-x)^binomial(n, 2)), n = 0 .. infinity). a(n) = Sum((-1)^(n-k)*Stirling1(n, k)*A020554(k), k=0..n). - Vladeta Jovovic (vladeta(AT)eunet.rs), May 02 2004
E.g.f.: exp(x/(2-2*x))*Sum(A020556(n)*(-ln(1-x)/2)^n/n!, n=0..infinity). - Vladeta Jovovic (vladeta(AT)eunet.rs), May 02 2004
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CROSSREFS
| Sequence in context: A052871 A104653 A194787 * A193467 A179494 A203157
Adjacent sequences: A020555 A020556 A020557 * A020559 A020560 A020561
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KEYWORD
| nonn
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AUTHOR
| Gilbert Labelle (gilbert(AT)lacim.uqam.ca), Simon Plouffe (simon.plouffe(AT)gmail.com)
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