44511042511domain: NAppears in sequencesNumber of partially ordered sets ("posets") with n labeled elements (or labeled acyclic transitive digraphs).at n=9A001035Triangular 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=44A247231