1864800domain: NAppears in sequencesa(n) = 4!*n*Stirling2(n-1,4).at n=10A052776Triangular array read by rows. T(n,k) is the number of chain topologies on an n-set with exactly k open sets where one of the open sets is a single point set, n >= 2, 3 <= k <= n+1.at n=39A282507