|
| |
|
|
A052760
|
|
A simple grammar.
|
|
0
| |
|
|
0, 0, 0, 0, 24, 120, 420, 1260, 3472, 9072, 22860, 56100, 134904, 319176, 745108, 1719900, 3931680, 8912352, 20053404, 44825940, 99613960
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 0,5
|
|
|
LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 717
|
|
|
FORMULA
| E.g.f.: x^2*exp(x)^2-2*exp(x)*x^2+x^2
Recurrence: {a(1)=0, a(2)=0, a(3)=0, a(4)=24, (2*n^2+6*n+4)*a(n)+(6-3*n^2-3*n)*a(n+1)+(n^2-n)*a(n+2)}
|
|
|
MAPLE
| spec := [S, {B=Set(Z, 1 <= card), S=Prod(B, B, Z, Z)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
|
|
|
CROSSREFS
| Sequence in context: A059775 A052762 A099317 * A179720 A052754 A050213
Adjacent sequences: A052757 A052758 A052759 * A052761 A052762 A052763
|
|
|
KEYWORD
| easy,nonn
|
|
|
AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
|
| |
|
|
