OFFSET
0,4
COMMENTS
The original name was: A simple grammar.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..10000
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 804
FORMULA
G.f.: (exp(Sum_{j>=1} -x^j/((x^j-1)*j) )-1)^2.
a(n) = Sum_{k>=2} A304789(n,k). - Alois P. Heinz, May 26 2018
MAPLE
spec := [S, {C=Sequence(Z, 1 <= card), B=Set(C, 1 <= card), S=Prod(B, B)}, unlabeled]: seq(combstruct[count](spec, size=n), n=0..20);
# second Maple program:
a:= n-> (p-> add(p(j)*p(n-j), j=1..n-1))(combinat[numbpart]):
seq(a(n), n=0..40); # Alois P. Heinz, May 26 2018
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
EXTENSIONS
More terms from Franklin T. Adams-Watters, Feb 08 2006
New name from Alois P. Heinz, May 26 2018
STATUS
approved