%I #7 Apr 23 2022 16:21:30
%S 1,2,16,190,2768,45584,814728,15439974,305760400,6265985440,
%T 131980086368,2843029539376,62400628835608,1391503990134080,
%U 31454839290752912,719470742267557110,16627360903974831120,387786053931422003360
%N a(n) = [x^n] (1-x)^(3n+1)/(n+1) * Sum_{k>=0} C(n+k-1,k)^3*x^k.
%F a(n) = A183204(n)/(n+1), where A183204 equals the central terms of triangle A181544.
%o (PARI) {a(n)=polcoeff((1-x)^(3*n+1)/(n+1)*sum(j=0, 2*n, binomial(n+j, j)^3*x^j), n)}
%Y Cf. A181544, A183204.
%K nonn
%O 0,2
%A _Paul D. Hanna_, Dec 30 2010