OFFSET
0,3
COMMENTS
Old name was: A simple grammar.
LINKS
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 732
FORMULA
G.f. A(x) satisfies: A(x) = exp( Sum_{k>=1} (-1)^(k+1) * A(x^k)^4 * x^k / k ). - Ilya Gutkovskiy, May 26 2023
MAPLE
spec := [S, {B=Prod(Z, S, S, S, S), S=PowerSet(B)}, unlabeled]: seq(combstruct[count](spec, size=n), n=0..20);
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
EXTENSIONS
New name from Ilya Gutkovskiy, May 26 2023
STATUS
approved