# A375810 (b-file synthesized from sequence entry) 0 1 1 2 2 6 3 30 4 192 5 1480 6 13500 7 141540 8 1676640 9 22141728 10 322388640 11 5130084960 12 88561408320 13 1648294876800 14 32898981155040 15 700940855815200 16 15877318955097600 17 380996919471168000 18 9654670629548904960 19 257627854786123261440 20 7220676423560766566400