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A093377 Number of labeled n-vertex graphs without 2-components and without isolated vertices (1-components). 1
1, 0, 0, 4, 38, 728, 26864, 1871576, 251762204, 66308767200, 34497665550400, 35641856042561008, 73354660691960203016, 301272244237002052739424, 2471648864359822034978330304, 40527681073171940835893232576032 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

Also number of unlabeled n-block ordered r-bicoverings, cf. A060053. - Vladeta Jovovic, May 13 2004

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..65

FORMULA

E.g.f. exp(-x-x^2/2)*Sum(2^binomial(n, 2)*x^n/n!, n=0..infinity).

Inverse binomial transform of A093352().

MATHEMATICA

nn=20; g=Sum[2^Binomial[n, 2]x^n/n!, {n, 0, nn}]; Range[0, nn]!CoefficientList[Series[Exp[ Log[g]-x-x^2/2!], {x, 0, nn}], x]  (* Geoffrey Critzer, Apr 15 2013 *)

PROG

(PARI) N=66; x='x+O('x^N);

egf=exp(-x-x^2/2)*sum(i=0, N, 2^binomial(i, 2)*x^i/i!);

Vec(serlaplace(egf))

/* Joerg Arndt, Jul 06 2011 */

CROSSREFS

Cf. A006129, A093351, A093352.

Sequence in context: A084285 A084286 A001187 * A178017 A131591 A030259

Adjacent sequences:  A093374 A093375 A093376 * A093378 A093379 A093380

KEYWORD

nonn

AUTHOR

Goran Kilibarda, Vladeta Jovovic, Apr 28 2004

STATUS

approved

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Last modified April 23 18:28 EDT 2019. Contains 322387 sequences. (Running on oeis4.)