login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A231601 Number of permutations of [n] avoiding ascents from odd to even numbers. 3
1, 1, 1, 4, 8, 54, 162, 1536, 6144, 75000, 375000, 5598720, 33592320, 592950960, 4150656720, 84557168640, 676457349120, 15620794116480, 140587147048320, 3628800000000000, 36288000000000000, 1035338990313196800, 11388728893445164800, 355902198372945100800 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..250

FORMULA

a(n) = ceiling(n/2)! * ceiling(n/2)^floor(n/2).

a(n) = A081123(n+1) * A110138(n).

EXAMPLE

a(0) = 1: ().

a(1) = 1: 1.

a(2) = 1: 21.

a(3) = 4: 132, 213, 231, 321.

a(4) = 8: 1324, 2413, 2431, 3241, 4132, 4213, 4231, 4321.

a(5) = 54: 13245, 13254, 13524, ..., 54213, 54231, 54321.

a(6) = 162: 132465, 132546, 132645, ..., 654213, 654231, 654321.

MAPLE

a:= n-> ceil(n/2)!*ceil(n/2)^floor(n/2):

seq(a(n), n=0..30);

CROSSREFS

Column k=0 of A231777.

Bisection gives: A061711 (even part).

Cf. A081123, A110138, A199660, A285672.

Sequence in context: A128893 A214603 A192508 * A123106 A123288 A192200

Adjacent sequences:  A231598 A231599 A231600 * A231602 A231603 A231604

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Nov 11 2013

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 January 29 08:12 EST 2020. Contains 331337 sequences. (Running on oeis4.)