OFFSET
1,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..100
FORMULA
a(n) ~ 2*sqrt(Pi*n)*2^n*n^(2*n)/exp(2*n+1). - Ilya Gutkovskiy, Aug 18 2016
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 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jul 08 2016
STATUS
approved