OFFSET
0,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..1000
FORMULA
Recurrence: (n+3)*(3*n-1)*a(n) = (6*n^2+19*n+7)*a(n-1) + 3*(n-1)*(3*n+2)*a(n-2). - Vaclav Kotesovec, Oct 08 2012
a(n) ~ 4*3^(n+1/2)/sqrt(Pi*n). - Vaclav Kotesovec, Oct 08 2012
MATHEMATICA
Table[Sum[(-1)^(n-k)*Binomial[n, k]*Binomial[2k+3, k], {k, 0, n}], {n, 0, 22}] (* Vaclav Kotesovec, Oct 08 2012 *)
PROG
(PARI) a(n)=sum(k=0, n, (-1)^(n-k)*binomial(n, k)*binomial(2*k+3, k) ); \\ Joerg Arndt, May 04 2013
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved