OFFSET
0,3
COMMENTS
Previous name was: A simple grammar.
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..424
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 799
FORMULA
E.g.f.: log(-1/(-2+exp(x)))^2.
a(n) ~ (n-1)! * 2*(log(n) + gamma - log(2) - log(log(2)))/log(2)^n, where gamma is Euler-Mascheroni constant (A001620). - Vaclav Kotesovec, Sep 30 2013
MAPLE
spec := [S, {B=Set(Z, 1 <= card), C=Cycle(B), S=Prod(C, C)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
MATHEMATICA
CoefficientList[Series[Log[2-E^x]^2, {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, Sep 30 2013 *)
PROG
(PARI) x='x+O('x^30); concat([0, 0], Vec(serlaplace((log(2-exp(x)))^2))) \\ G. C. Greubel, Sep 05 2018
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
EXTENSIONS
New name, using e.g.f., by Vaclav Kotesovec, Sep 30 2013
More terms from Alois P. Heinz, Mar 16 2016
STATUS
approved