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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

Table of n, a(n) for n=0..15.

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.)