# A373773 (b-file synthesized from sequence entry) 0 1 1 1 2 2 3 7 4 36 5 240 6 1930 7 17990 8 189840 9 2233000 10 28949200 11 410009600 12 6297999400 13 104275571400 14 1851050401200 15 35065930299400 16 705993054166400 17 15051593241484800 18 338705933426660800 19 8021585392026606400 20 199416162740963168000 21 5191567315003621552000