773094113280domain: NAppears in sequencesTriangular array read by rows. T(n,k) is the number of k-colored labeled digraphs with n vertices, n>=1, 1<=k<=n.at n=20A240955Order of the symplectic group of 4 X 4 matrices over Z_n.at n=15A364771a(n) = n! * 4^binomial(n, 2).at n=6A376868