|
Search: id:A000449
|
|
|
| A000449 |
|
Rencontres numbers: permutations with exactly 3 fixed points.
(Formerly M4700 N2009)
|
|
+0
9
|
|
| 1, 0, 10, 40, 315, 2464, 22260, 222480, 2447445, 29369120, 381798846, 5345183480, 80177752655, 1282844041920, 21808348713320, 392550276838944, 7458455259940905, 149169105198816960, 3132551209175157490, 68916126601853463240
(list; graph; listen)
|
|
|
OFFSET
|
3,3
|
|
|
REFERENCES
|
J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, p. 65.
|
|
FORMULA
|
a(n)=sum((-1)^j*n!/(3!*j!), j=2..n-3).
For n >= 3 a(n) = C(n, 3) * A000166(n-3) = 1/6 * n! * sum((-1)^k /k!, k=0..n-3). - Dan Fux (dan.fux(AT)OpenGaia.com or danfux(AT)OpenGaia.com), Apr 14 2001
|
|
MAPLE
|
a:=n->sum(n!*sum((-1)^k/(k-2)!, j=0..n), k=2..n): seq(a(n)/3!, n=2..21); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), May 25 2007
|
|
CROSSREFS
|
Cf. A000240, A000387, A000475.
A diagonal of A008291.
Sequence in context: A060580 A118266 A054885 this_sequence A027274 A012868 A016082
Adjacent sequences: A000446 A000447 A000448 this_sequence A000450 A000451 A000452
|
|
KEYWORD
|
nonn,easy
|
|
AUTHOR
|
njas
|
|
|
Search completed in 0.002 seconds
|
