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A simple grammar: product of cycles and cycles of cycles.
1

%I #14 Apr 18 2017 07:04:09

%S 0,0,2,9,48,315,2497,23394,254132,3149826,43945354,682314028,

%T 11676044036,218402171520,4433885571840,97098961376112,

%U 2281563329170752,57255174735315792,1528204674443305680,43227315891291907488,1291646719998952196448,40652195494651491747840

%N A simple grammar: product of cycles and cycles of cycles.

%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=791">Encyclopedia of Combinatorial Structures 791</a>

%F E.g.f.: log(-1/(-1+x))*log(-1/(-1+log(-1/(-1+x)))).

%p spec := [S,{B=Cycle(C),C=Cycle(Z),S=Prod(C,B)},labeled]: seq(combstruct[count](spec,size=n), n=0..20);

%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