|
| |
|
|
A052747
|
|
a(0) = a(1) = a(2) = 0; a(n) = n!/(n-2) for n > 2.
|
|
3
| |
|
|
0, 0, 0, 6, 12, 40, 180, 1008, 6720, 51840, 453600, 4435200, 47900160, 566092800, 7264857600, 100590336000, 1494484992000, 23712495206400, 400148356608000, 7155594141696000, 135161222676480000
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 0,4
|
|
|
COMMENTS
| A simple grammar.
|
|
|
LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 703
|
|
|
FORMULA
| E.g.f.: ln(-1/(-1+x))*x^2
Recurrence: {a(0)=0, a(1)=0, a(2)=0, a(3)=6, (n+2-n^2)*a(n)+(n-1)*a(n+1)}
|
|
|
MAPLE
| spec := [S, {B=Cycle(Z), S=Prod(Z, Z, B)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
|
|
|
PROG
| (PARI) a(n)=if(n>2, n!/(n-2), 0) \\ Charles R Greathouse IV, Nov 20 2011
|
|
|
CROSSREFS
| Contribution from Johannes W. Meijer (meijgia(AT)hotmail.com), Jul 21 2009: (Start)
Equals the square root of the second right hand column of A162990 for n=>3.
(End)
Sequence in context: A026083 A128453 A185616 * A007121 A152786 A206039
Adjacent sequences: A052744 A052745 A052746 * A052748 A052749 A052750
|
|
|
KEYWORD
| easy,nonn
|
|
|
AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
|
|
|
EXTENSIONS
| Better description from Olivier Gerard (olivier.gerard(AT)gmail.com), Jun 13 2001
|
| |
|
|
