%I #14 May 27 2023 05:48:42
%S 1,1,3,15,79,466,2872,18409,121197,815491,5581214,38737651,272012178,
%T 1928939678,13794498614,99371002295,720411445866,5252194141946,
%U 38482834469488,283223825607253,2092829973445703
%N G.f. A(x) satisfies: A(x) = exp( Sum_{k>=1} (-1)^(k+1) * A(x^k)^3 * x^k / k )
%C Old name was: A simple grammar.
%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=711">Encyclopedia of Combinatorial Structures 711</a>
%F G.f. A(x) satisfies: A(x) = exp( Sum_{k>=1} (-1)^(k+1) * A(x^k)^3 * x^k / k ). - _Ilya Gutkovskiy_, May 26 2023
%p spec := [S,{S=PowerSet(B),B=Prod(S,S,S,Z)},unlabeled]: seq(combstruct[count](spec,size=n), n=0..20);
%Y Cf. A005754, A052775, A052798.
%K easy,nonn
%O 0,3
%A encyclopedia(AT)pommard.inria.fr, Jan 25 2000
%E New name from _Ilya Gutkovskiy_, May 26 2023