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%I #17 Apr 18 2017 07:04:09
%S 0,0,2,6,34,220,1808,17388,194724,2478096,35418192,561533280,
%T 9785418432,185921027136,3825633439392,84756646285920,
%U 2011657535668128,50924796197369088,1369659967551038976,39003791158314816768,1172394903935534452992,37094744191300029964800
%N A simple grammar: cycles of pairs of cycles.
%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=789">Encyclopedia of Combinatorial Structures 789</a>
%F E.g.f.: log(-1/(-1+log(-1/(-1+x))^2)).
%F E.g.f.: -log(1-(log(1-x))^2). - _Vaclav Kotesovec_, Oct 01 2013
%F a(n) ~ (n-1)! * (exp(1)/(exp(1)-1))^n. - _Vaclav Kotesovec_, Oct 01 2013
%p spec := [S,{B=Cycle(Z),C=Prod(B,B),S=Cycle(C)},labeled]: seq(combstruct[count](spec,size=n), n=0..20);
%t CoefficientList[Series[-Log[1-(Log[1-x])^2], {x, 0, 20}], x]* Range[0, 20]! (* _Vaclav Kotesovec_, Oct 01 2013 *)
%Y Cf. A185393.
%K easy,nonn
%O 0,3
%A encyclopedia(AT)pommard.inria.fr, Jan 25 2000
%E More terms from _Alois P. Heinz_, Mar 16 2016
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