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 A014505 Number of digraphs with unlabeled (non-isolated) nodes and n labeled edges. 7
 1, 1, 6, 68, 1206, 29982, 981476, 40515568, 2044492988, 123175320988, 8697475219688, 709097832452880, 65934837808883016, 6920436929999656936, 812724019581549433520, 105986960037601701495680 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 REFERENCES G. Labelle, Counting enriched multigraphs..., Discrete Math., 217 (2000), 237-248. G. Paquin, Dénombrement de multigraphes enrichis, Mémoire, Math. Dept., Univ. Québec à Montréal, 2004. LINKS G. Paquin, Dénombrement de multigraphes enrichis, Mémoire, Math. Dept., Univ. Québec à Montréal, 2004. [Cached copy, with permission] FORMULA E.g.f.: exp(-1) * Sum_{n>=0} (1+x)^(n^2-n) / n!. - Paul D. Hanna, Apr 25 2018 a(n) = n!*exp(-1) * Sum_{k>=sqrt(n)} binomial(k^2-k, n) / k!. - Paul D. Hanna, Apr 25 2018 CROSSREFS Cf. A014507. Sequence in context: A256238 A349557 A140606 * A274722 A347927 A127184 Adjacent sequences:  A014502 A014503 A014504 * A014506 A014507 A014508 KEYWORD nonn AUTHOR Simon Plouffe, gilbert(AT)lacim.uqam.ca (Gilbert Labelle). STATUS approved

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Last modified November 30 18:40 EST 2021. Contains 349424 sequences. (Running on oeis4.)