OFFSET
0,2
COMMENTS
Previous name was: A simple grammar.
LINKS
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 770
FORMULA
E.g.f.: -log(1-x+log(1-x)). - Michael Somos, Sep 21, 2002
a(n) ~ (n-1)! / (1-LambertW(1))^n. - Vaclav Kotesovec, Oct 01 2013
MAPLE
spec := [S, {C=Cycle(Z), B=Union(C, Z), S=Cycle(B)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
MATHEMATICA
With[{nn=30}, CoefficientList[Series[-Log[1-x+Log[1-x]], {x, 0, nn}], x] Range[ 0, nn]!] (* Harvey P. Dale, Mar 27 2013 *)
PROG
(PARI) a(n)=if(n<0, 0, n!*polcoeff(-log(1-x+log(1-x+x*O(x^n))), n))
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
EXTENSIONS
More terms from Harvey P. Dale, Mar 27 2013
New name, using e.g.f., by Vaclav Kotesovec, Oct 01 2013
STATUS
approved