# A003268 (b-file synthesized from sequence entry) 0 1 1 2 2 6 3 15 4 60 5 260 6 1820 7 12376 8 136136 9 1514513 10 27261234 11 488605194 12 14169550626 13 411591708660 14 19344810307020 15 908637119420910 16 69056421075989160 17 5249543573067466872 18 645693859487298425256 19 79413089729752455762384 20 15803204856220738696714416