A001188 Number of even graphs with n edges. (Formerly M1892 N0746)

1, 2, 8, 60, 672, 9953, 184557, 4142631, 109813842, 3373122370, 118280690398, 4678086540493, 206625802351035, 10107719377251109, 543762148079927802, 31975474310851749920, 2044501883873268414092, 141485408653554069693421

Offset

1,2

Comments

a(n) appears to be [A060639(n) + 1] / 2. - Ralf Stephan, Aug 21 2004

References

D. G. Cantor, personal communication.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

Sean A. Irvine, Table of n, a(n) for n = 1..50

E. N. Gilbert, Enumeration of labelled graphs, Canad. J. Math., 8 (1956), 405-411.

E. N. Gilbert, Enumeration of labelled graphs (Annotated scanned copy)

R. W. Robinson, First 50 terms of A1187 and A1188

Maple

with(combinat);
g:=k->sum(stirling2(k, j), j=0..k)^2;
egf:=series((exp(x)-1+log(1+sum(g(k)*x^k/k!, k=1..infinity)))/2, x, 20);
seq(n!*coeff(egf, x, n), n=1..20); # Sean A. Irvine, Mar 22 2012

Crossrefs

Sequence in context: A052622 A303672 A303062 * A355100 A303532 A355106

Adjacent sequences: A001185 A001186 A001187 * A001189 A001190 A001191

Keyword

nonn

Author

N. J. A. Sloane

Extensions

More terms from Sean A. Irvine, Mar 21 2012

Status

approved