OFFSET
1,2
LINKS
D. Callan, Divisibility of a Central Binomial Sum: A11292 and A11307, Amer. Math. Monthly, 116 (2009), 468-470.
FORMULA
a(n) ~ 4^(n^2) / (3*sqrt(Pi)*n). - Vaclav Kotesovec, Jun 07 2019
MATHEMATICA
Table[Sum[Binomial[2*k, k], {k, 1, n^2 - 1}], {n, 1, 10}] (* Vaclav Kotesovec, Jun 07 2019 *)
PROG
(PARI) a(n) = sum(k=1, n^2-1, binomial(2*k, k)); \\ Michel Marcus, Jul 05 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Apr 25 2009
STATUS
approved