|
Search: id:A052521
|
|
|
| A052521 |
|
Number of pairs of sequences of cardinality at least 3. |
|
+0
1
|
|
| 0, 0, 0, 0, 0, 0, 720, 10080, 120960, 1451520, 18144000, 239500800, 3353011200, 49816166400, 784604620800, 13076743680000, 230150688768000, 4268249137152000, 83230858174464000, 1703031405723648000
(list; graph; listen)
|
|
|
OFFSET
|
0,7
|
|
|
LINKS
|
Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 88
|
|
FORMULA
|
E.g.f.: x^6/(-1+x)^2
Recurrence: {a(1)=0, a(0)=0, a(2)=0, a(4)=0, a(3)=0, a(5)=0, (-n^2+3*n+4)*a(n)+(n-5)*a(n+1), a(6)=720}
(n-5)*n!
|
|
MAPLE
|
Pairs spec := [S, {B=Sequence(Z, 3 <= card), S=Prod(B, B)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
|
|
CROSSREFS
|
Sequence in context: A052786 A052792 A052790 this_sequence A052785 A052783 A112002
Adjacent sequences: A052518 A052519 A052520 this_sequence A052522 A052523 A052524
|
|
KEYWORD
|
easy,nonn
|
|
AUTHOR
|
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
|
|
|
Search completed in 0.002 seconds
|
