OFFSET
0,3
COMMENTS
Previous name was: A simple grammar.
LINKS
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 833
FORMULA
E.g.f.: log(-1/(-1+x))^2 / (-1 + log(-1/(-1+x)))^2.
a(n) = sum(k=1..n, (k-1)*k!*(-1)^(n-k)*Stirling1(n,k)). - Vladimir Kruchinin, Sep 26 2011
a(n) ~ n! * exp(n)*n/(exp(1)-1)^(n+2). - Vaclav Kotesovec, Sep 29 2013
MAPLE
spec := [S, {C=Cycle(Z), B=Sequence(C, 1 <= card), S=Prod(B, B)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
MATHEMATICA
CoefficientList[Series[Log[-1/(-1+x)]^2/(-1+Log[-1/(-1+x)])^2, {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, Sep 29 2013 *)
PROG
(Maxima) a(n):=sum((k-1)*k!*(-1)^(n-k)*stirling1(n, k), k, 1, n); /* Vladimir Kruchinin, Sep 26 2011 */
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
EXTENSIONS
New name using e.g.f., Joerg Arndt, Sep 30 2013
STATUS
approved