|
| |
|
|
A052693
|
|
E.g.f. (1-x)/(1-3x+x^3).
|
|
0
| |
|
|
1, 2, 12, 102, 1176, 16920, 292320, 5891760, 135717120, 3517032960, 101268921600, 3207514464000, 110828037196800, 4148515981209600, 167232459621427200, 7222900141416960000, 332760193091149824000
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 0,2
|
|
|
LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 642
|
|
|
FORMULA
| E.g.f.: -(-1+x)/(1-3*x+x^3)
Recurrence: {a(0)=1, a(1)=2, (n^3+6*n^2+11*n+6)*a(n)+(-3*n-9)*a(n+2)+a(n+3)=0, a(2)=12}
Sum(-1/9*(-2+_alpha^2-_alpha)*_alpha^(-1-n), _alpha=RootOf(1-3*_Z+_Z^3))*n!
|
|
|
MAPLE
| spec := [S, {S=Sequence(Union(Z, Prod(Z, Union(Z, Sequence(Z)))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
|
|
|
CROSSREFS
| Sequence in context: A137483 A113557 A123897 * A050621 A152254 A157328
Adjacent sequences: A052690 A052691 A052692 * A052694 A052695 A052696
|
|
|
KEYWORD
| easy,nonn
|
|
|
AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
|
| |
|
|
