A052824 A simple grammar: cycles of pairs of cycles.

0, 0, 2, 6, 34, 220, 1808, 17388, 194724, 2478096, 35418192, 561533280, 9785418432, 185921027136, 3825633439392, 84756646285920, 2011657535668128, 50924796197369088, 1369659967551038976, 39003791158314816768, 1172394903935534452992, 37094744191300029964800

Offset: 0

Author

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

Keywords

• easy
• nonn

Links

• INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 789

Crossrefs

Cf. A185393.

Programs

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 *)

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

Extensions

More terms from Alois P. Heinz, Mar 16 2016