A052708 A simple context-free grammar.

0, 0, 1, 2, 5, 16, 56, 204, 768, 2970, 11726, 47060, 191412, 787304, 3269100, 13684864, 57691353, 244713654, 1043684478, 4472828400, 19252045120

Offset

0,4

Links

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

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 663

Formula

G.f.: RootOf(-_Z+_Z^4+_Z^2+x)^2

Recurrence: {a(1)=0, a(2)=1, a(3)=2, a(4)=5, (-576-1920*n+3072*n^2+6144*n^3)*a(n)+(-9096-30320*n-28032*n^2-7936*n^3)*a(n+1)+(41380*n+20808+28032*n^2+6272*n^3)*a(n+2)+(-26520*n^2-60704*n-45600-3784*n^3)*a(n+3)+(589*n^3+5301*n^2+15314*n+14136)*a(n+4)}

Maple

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

Crossrefs

Sequence in context: A102461 A176332 A191241 * A149973 A149974 A149975

Adjacent sequences: A052705 A052706 A052707 * A052709 A052710 A052711

Keyword

easy,nonn

Author

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

Status

approved