6129859

Appears in sequences

• Number of partially ordered sets ("posets") with n labeled elements (or labeled acyclic transitive digraphs).at n=7A001035
• Number of prime labeled T_0 topologies on n points.at n=5A028854
• Triangular array read by rows: T(n,k) is the number of transitive relations on {1,2,...,n} that have exactly k reflexive points, n>=0, 0<=k<=n.at n=28A245767
• Triangular array read by rows: T(n,k) is the number of ways to partition an n-set into exactly k blocks and then partially order the blocks, n>=1, 1<=k<=n.at n=27A247231
• Triangle read by rows: T(n,k) = number of topologies on an n-set X such that there are exactly k elements in X that are topologically distinguishable, n >= 0, 0 <= k <= n.at n=35A280192
• Triangular array read by rows. T(n,k) is the number of inequivalent (as defined below) transitive binary relations R on [n] such that |domain(R intersect R^(-1))| = k, n>=0, 0<=k<=n.at n=28A369776