A182157 The number of simple unlabelled graphs with n nodes having no components of size 1 or 2.

2, 6, 21, 115, 865, 11180, 261434, 11719198, 1006730374, 164060444228, 50335933202664, 29003489553692808, 31397381477206877920, 63969560214904127718624, 245871831740396590978751568, 1787331725311868949057440884912, 24636021429527995774854054487417072, 645465483199214927570182087868056845600

Offset

3,1

Links

Table of n, a(n) for n=3..20.

Formula

O.g.f.: (1-x)*(1-x^2)* G(x) where G(x) is o.g.f. for A000088

Mathematica

nn = 20; g = Sum[NumberOfGraphs[n] x^n, {n, 0, nn}]; Drop[CoefficientList[Series[ g (1 - x) (1 - x^2), {x, 0, nn}], x], 3]

Crossrefs

Sequence in context: A001349 A126060 A266934 * A356015 A110306 A351691

Adjacent sequences: A182154 A182155 A182156 * A182158 A182159 A182160

Keyword

nonn

Author

Geoffrey Critzer, Apr 15 2012

Status

approved