a(n) = (3*n+1)!*(3*n)!/((2*n)!*((n+1)!)^2).A383874a(n) = (3*n+1)!*(3*n)!/((2*n)!*((n+1)!)^2).Terms a(0) =1a(1) =18a(2) =4200a(3) =3175200a(4) =5137292160External referencesoeis: A383874