|
Search: id:A145219
|
|
|
| A145219 |
|
a(n) is the number of even permutations (of an n-set) with exactly 1 fixed point. |
|
+0
2
|
|
| 1, 0, 0, 8, 15, 144, 910, 7440, 66717, 667520, 7342236, 88107480, 1145396395, 16035550608
(list; graph; listen)
|
|
|
OFFSET
|
1,4
|
|
|
REFERENCES
|
Ali, Bashir and Umar, A., "Some combinatorial properties of the alternating group". Southeast Asian Bulletin Math. 32 (2008), 823-830.
|
|
FORMULA
|
a(n)=n*A003221(n-1), (n > 0).
Egf.: (x(1-x^2/2)e^(-x))/(1-x)
|
|
EXAMPLE
|
a(4) = 8 because there are exactly 8 even permutations (of a 4-set) having 1 fixed point, namely: (123), (132), (124), (142), (134), (143), (234), (243).
|
|
CROSSREFS
|
A003221
Sequence in context: A110459 A132374 A067686 this_sequence A002406 A153700 A066916
Adjacent sequences: A145216 A145217 A145218 this_sequence A145220 A145221 A145222
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
A. Umar (aumarh(AT)squ.edu.om), Oct 09 2008
|
|
|
Search completed in 0.002 seconds
|
