OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..200
FORMULA
a(n) = 1/n * Sum_{j=0..n-1} C(3*n,j)*(n-j)*6^j for n>0, a(0) = 1.
Recurrence: n*(2*n-1)*(5*n-6)*a(n) = (3835*n^3 - 7127*n^2 + 3201*n - 180)*a(n-1) - 3087*(3*n-5)*(3*n-4)*(5*n-1)*a(n-2). - Vaclav Kotesovec, Aug 31 2014
a(n) ~ 3^(4*n+3/2) / (121 * 2^(n-1) * sqrt(Pi) * n^(3/2)). - Vaclav Kotesovec, Aug 31 2014
MAPLE
a:= n-> `if`(n=0, 1, add(binomial(3*n, j)*(n-j)*6^j, j=0..n-1)/n):
seq(a(n), n=0..20);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Oct 29 2012
STATUS
approved