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A052828
A simple grammar: union of cycles and cycles of cycles.
0
0, 2, 3, 9, 41, 252, 1954, 18302, 200906, 2528152, 35862456, 565985472, 9834073248, 186504365616, 3833188731072, 84862243895088, 2013237501351504, 50950031663224320, 1370088133344414336, 39011485705595544960, 1172540863138831491456, 37097659139410654988544
OFFSET
0,2
FORMULA
E.g.f.: log(-1/(-1+x))+log(-1/(-1+log(-1/(-1+x)))).
MAPLE
spec := [S, {B=Cycle(C), C=Cycle(Z), S=Union(C, B)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
CROSSREFS
Sequence in context: A125052 A181139 A162093 * A214915 A219673 A012972
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
EXTENSIONS
More terms from Alois P. Heinz, Mar 16 2016
STATUS
approved