A226285 a(n) = [n/2]!*[(n+1)/2]!*C([n/2],4)*C([(n+1)/2],4).

0, 0, 0, 0, 0, 0, 0, 576, 14400, 360000, 6480000, 116640000, 1905120000, 31116960000, 497871360000, 7965941760000, 129048256512000, 2090581755494400, 34843029258240000, 580717154304000000, 10038110810112000000, 173515915431936000000, 3123286477774848000000

Offset: 1

Author

R. H. Hardin, connection of formula with combinatoric problem via N. J. A. Sloane in the Sequence Fans Mailing List, Jun 02 2013

Keywords

• nonn

Comments

Number of permutations of n elements with 8 odd displacements.

Column 5 of A226288.

Column k=8 of A145893, a diagonal of A145894. - Alois P. Heinz, May 29 2014

Links

• R. H. Hardin, Table of n, a(n) for n = 1..210

Crossrefs

Cf. A145893, A145894, A226288.

Programs

Mathematica

a[n_]:= Floor[n/2]!*Floor[(n+1)/2]!*Binomial[Floor[n/2],4]*Binomial[Floor[(n+1)/2],4]; Array[a,21] (* Stefano Spezia, Jul 12 2024 *)