OFFSET
0,2
FORMULA
a(n) = (binomial(1 + 3*n, n)*2F1([1, -n], [-1 - 3*n], 1 + n)/(1 + n), where 2F1 is the hypergeometric function.
a(n) ~ exp(3) * n^(n-1). - Vaclav Kotesovec, Nov 06 2019
MATHEMATICA
Table[(Binomial[1+3n, n]Hypergeometric2F1[1, -n, -1-3n, 1+n])/(1+n), {n, 0, 19}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Stefano Spezia, Nov 05 2019
STATUS
approved