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A simple grammar.
1

%I #17 Jul 05 2017 02:02:56

%S 0,1,2,5,14,42,138,466,1643,5919,21773,81279,307483,1175352,4534161,

%T 17626999,68992703,271641249,1075144364,4275274867,17071822275,

%U 68428152475,275217386092,1110375948303,4492641333003,18225081419544,74111194585752,302040709982249

%N A simple grammar.

%H Robert Israel, <a href="/A052853/b052853.txt">Table of n, a(n) for n = 0..1000</a>

%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=821">Encyclopedia of Combinatorial Structures 821</a>

%F G.f. appears to be -Sum_{j>=1} (phi(j)/j) * log(1-C(x^j)), where phi = A000010 and C is the g.f. of A050383. - _Robert Israel_, Nov 01 2016

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

%Y Cf. A000010, A050383.

%K easy,nonn

%O 0,3

%A encyclopedia(AT)pommard.inria.fr, Jan 25 2000