A052708 - OEIS

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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

(list; graph; refs; listen; history; text; internal format)

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