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The number of simple unlabelled graphs with n nodes having no components of size 1 or 2.
0

%I #8 Apr 16 2012 10:58:41

%S 2,6,21,115,865,11180,261434,11719198,1006730374,164060444228,

%T 50335933202664,29003489553692808,31397381477206877920,

%U 63969560214904127718624,245871831740396590978751568,1787331725311868949057440884912,24636021429527995774854054487417072,645465483199214927570182087868056845600

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

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

%t 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]

%K nonn

%O 3,1

%A _Geoffrey Critzer_, Apr 15 2012