1723680domain: NAppears in sequencesA simple context-free grammar in a labeled universe: labeled version of A052705.at n=7A052728Triangular 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=33A282507