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

1,3

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

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 *)

Crossrefs

Cf. A145893, A145894, A226288.

Sequence in context: A327541 A158784 A180141 * A013991 A151245 A151246

Adjacent sequences: A226279 A226280 A226281 * A226283 A226284 A226285

Keyword

nonn

Author

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

Status

approved