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%I #18 Jul 27 2016 19:26:57
%S 1,0,3,16,376,13292,933488,125771776,33148165696,17248244115968,
%T 17820828776291072,36677298103363352704,150636101324832283976704,
%U 1235824405515221864531935232,20263840468865240117348466818048,664289479167891600504168839585529856
%N Number of connected labeled graphs with n nodes and an even number of edges.
%H V. A. Liskovets, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL3/LISK/Derseq.html">Some easily derivable sequences</a>, J. Integer Sequences, 3 (2000), #00.2.2.
%F a(n) = (A001187(n)+(-1)^(n-1)*A000142(n-1))/2.
%t nn = 15; Clear[f];f[z_] := Sum[(1 + u)^Binomial[n, 2] z^n/n!, {n, 0, nn + 1}]; Drop[Map[Total[#[[1 ;; Binomial[nn, 2] ;; 2]]] &,Range[0, nn]! CoefficientList[Series[ Log[f[z]] , {z, 0, nn}], {z, u}]], 1] (* _Geoffrey Critzer_, Jul 27 2016 *)
%K nonn,easy
%O 1,3
%A _N. J. A. Sloane_, May 24 2000
%E More terms from _Vladeta Jovovic_, Jul 17 2000
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