login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A145224 Triangle read by rows: T(n,k) is the number of even permutations (of an n-set) with exactly k fixed points. 0
1, 0, 1, 0, 0, 1, 2, 0, 0, 1, 3, 8, 0, 0, 1, 24, 15, 20, 0, 0, 1, 130, 144, 45, 40, 0, 0, 1, 930, 910, 504, 105, 70, 0, 0, 1, 7413, 7440, 3640, 1344, 210, 112, 0, 0, 1, 66752, 66717, 33480, 10920, 3024, 378, 168, 0, 0, 1 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

0,7

LINKS

Table of n, a(n) for n=0..54.

Bashir Ali and A. Umar, Some combinatorial properties of the alternating group, Southeast Asian Bulletin Math. 32 (2008), 823-830.

FORMULA

T(n,k) = C(n,k)*A003221(n-k).

E.g.f.: (x^k(1-x^2/2) e^(-x))/k!(1-x).

EXAMPLE

Triangle starts:

1;

0, 1;

0, 0, 1;

2, 0, 0, 1;

3, 8, 0, 0, 1;

24, 15, 20, 0, 0;

...

CROSSREFS

Row sums give A001710, T(n,0) is A003221, T(n,1) is A145219, T(n,2) is A145220.

Sequence in context: A242464 A273185 A259784 * A138157 A073429 A123634

Adjacent sequences:  A145221 A145222 A145223 * A145225 A145226 A145227

KEYWORD

nonn,tabl

AUTHOR

Abdullahi Umar, Oct 09 2008

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 20 17:43 EDT 2019. Contains 324234 sequences. (Running on oeis4.)