A052703 A simple context-free grammar.

0, 0, 0, 1, 3, 12, 49, 210, 927, 4191, 19305, 90285, 427570, 2046324, 9881862, 48090824, 235619133, 1161257580, 5753365015, 28638093270, 143148398085

Offset

0,5

Links

Table of n, a(n) for n=0..20.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 656

Formula

G.f.: RootOf(-_Z+_Z^2+_Z^3+x)-RootOf(-_Z+_Z^2+_Z^3+x)^2-x

Recurrence: {a(1)=0, a(2)=0, a(3)=1, a(4)=3, (30-135*n+135*n^2)*a(n)+(-130-107*n+29*n^2)*a(n+1)+(-281*n-198-91*n^2)*a(n+2)+(15*n^2+75*n+90)*a(n+3)}

Maple

spec := [S, {C=Prod(B, B), B=Union(S, C, Z), S=Prod(B, C)}, unlabeled]: seq(combstruct[count](spec, size=n), n=0..20);

Crossrefs

Sequence in context: A012864 A045890 A049673 * A151170 A151171 A151172

Adjacent sequences: A052700 A052701 A052702 * A052704 A052705 A052706

Keyword

easy,nonn

Author

encyclopedia(AT)pommard.inria.fr, Jan 25 2000

Status

approved