OFFSET
0,3
COMMENTS
Previous name was: A simple grammar.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..1000
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 729
FORMULA
a(n) ~ c * d^n / n^(3/2), where d = 10.68849275496965245845204879846824293047921245695819153804780100052532088..., c = 0.097992887955331161579155538221616838965194192139... . - Vaclav Kotesovec, Feb 24 2015
From Ilya Gutkovskiy, Apr 13 2019: (Start)
G.f. A(x) satisfies: A(x) = x*exp(4*Sum_{k>=1} (-1)^(k+1)*A(x^k)/k).
G.f.: A(x) = Sum_{n>=1} a(n)*x^n = x * Product_{n>=1} (1 + x^n)^(4*a(n)). (End)
MAPLE
spec := [S, {S=Prod(Z, B, B, B, B), B=PowerSet(S)}, 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 Vaclav Kotesovec, Feb 24 2015
STATUS
approved