32179283136domain: NAppears in sequencesa(n) = Sum_{x_1+x_2+x_3+x_4=n, 0 <= x_1, x_2, x_3, x_4 <= n} (3*n)!/((n-x_1)! * (n-x_2)! * (n-x_3)! * (n-x_4)!).at n=6A348700