Number of symmetric difference-closed 4-sets consisting of the empty set and sets consisting of pairwise disjoint 2-subsets of {1,2,...,n}.

A267840

Number of symmetric difference-closed 4-sets consisting of the empty set and sets consisting of pairwise disjoint 2-subsets of {1,2,...,n}.

Terms

    a(0) =0a(1) =0a(2) =0a(3) =3a(4) =15a(5) =105a(6) =525a(7) =3255a(8) =17703a(9) =112455a(10) =669735a(11) =4485195a(12) =29023995a(13) =205768563a(14) =1432735395a(15) =10728177915a(16) =79665069435a(17) =627587657595

External references