a(n) = (n + 1/3) * (3*n + 3)! / ((n + 1)!)^3.

A360607

a(n) = (n + 1/3) * (3*n + 3)! / ((n + 1)!)^3.

Terms

    a(0) =2a(1) =120a(2) =3920a(3) =115500a(4) =3279276a(5) =91483392a(6) =2527462080a(7) =69413752980

External references