A052743 E.g.f. ( 1-x-sqrt(1-2*x+x^2-4*x^3) )/(2*x^2).

0, 1, 2, 6, 48, 480, 5040, 65520, 1048320, 18869760, 377395200, 8462361600, 209802700800, 5666588928000, 165900288153600, 5242466541312000, 177718177308672000, 6430828699975680000, 247490157968621568000

Offset

0,3

Links

Table of n, a(n) for n=0..18.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 699

Formula

D-finite with recurrence: a(1)=1; a(3)=6; a(2)=2; a(4)=48; (-56*n^2-26*n^3-12-46*n-4*n^4)*a(n) +(n^3+7*n^2+16*n+12)*a(n+1) +(-13*n-2*n^2-21)*a(n+2) +(n+5)*a(n+3) =0.

Maple

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

Crossrefs

Sequence in context: A292934 A195203 A365285 * A052587 A052735 A365286

Adjacent sequences: A052740 A052741 A052742 * A052744 A052745 A052746

Keyword

easy,nonn

Author

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

Status

approved