A226282 a(n) = [n/2]!*[(n+1)/2]!*C([n/2],1)*C([(n+1)/2],1).

0, 1, 4, 16, 72, 324, 1728, 9216, 57600, 360000, 2592000, 18662400, 152409600, 1244678400, 11379916800, 104044953600, 1053455155200, 10666233446400, 118513704960000, 1316818944000000, 15933509222400000, 192795461591040000, 2523867860828160000, 33039724723568640000

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 2 odd displacements.

Column 2 of A226288.

Column k=2 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

Table[Floor[n/2]!Floor[(n+1)/2]!Binomial[Floor[n/2],1]Binomial[Floor[(n+1)/2],1],{n,30}] (* Harvey P. Dale, Aug 05 2023 *)