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A052824 A simple grammar: cycles of pairs of cycles. 1
0, 0, 2, 6, 34, 220, 1808, 17388, 194724, 2478096, 35418192, 561533280, 9785418432, 185921027136, 3825633439392, 84756646285920, 2011657535668128, 50924796197369088, 1369659967551038976, 39003791158314816768, 1172394903935534452992, 37094744191300029964800 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..21.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 789

FORMULA

E.g.f.: log(-1/(-1+log(-1/(-1+x))^2)).

E.g.f.: -log(1-(log(1-x))^2). - Vaclav Kotesovec, Oct 01 2013

a(n) ~ (n-1)! * (exp(1)/(exp(1)-1))^n. - Vaclav Kotesovec, Oct 01 2013

MAPLE

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

MATHEMATICA

CoefficientList[Series[-Log[1-(Log[1-x])^2], {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, Oct 01 2013 *)

CROSSREFS

Cf. A185393.

Sequence in context: A346189 A018953 A009199 * A019029 A019032 A108424

Adjacent sequences:  A052821 A052822 A052823 * A052825 A052826 A052827

KEYWORD

easy,nonn

AUTHOR

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

EXTENSIONS

More terms from Alois P. Heinz, Mar 16 2016

STATUS

approved

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Last modified August 14 09:27 EDT 2022. Contains 356110 sequences. (Running on oeis4.)