A274634 a(n) = n!*A003436(n).

0, 2, 24, 744, 35160, 2394720, 222712560, 27154350720, 4205374225920, 806700010233600, 187793061031699200, 52162131258836121600, 17043501717850146739200, 6471785359791584459827200, 2826261760629911644744704000, 1406604814631643298586923008000

Offset: 1

Author

N. J. A. Sloane, Jul 08 2016

Keywords

• nonn

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..100

Crossrefs

Cf. A003436.

Programs

Mathematica

a[n_]:= n! (2 n - 1)!! Hypergeometric1F1[-n, 1 - 2 n, - 2]; a[1] = 0; Table[a[n], {n, 1, 20}] (* Vincenzo Librandi, Aug 18 2016 *)

Formula

a(n) ~ 2*sqrt(Pi*n)*2^n*n^(2*n)/exp(2*n+1). - Ilya Gutkovskiy, Aug 18 2016