60084domain: NAppears in sequencesa(n) = (2/n^3) * Sum_{d|n} moebius(n/d)*binomial(3*d,d).at n=9A268618Number of unlabeled directed graphs on n nodes without a subgraph isomorphic to directed K_{2,2} that have the maximal number of edges (=A191873(n)).at n=11A351335