# A008465 (b-file synthesized from sequence entry) 3 1 4 12 5 120 6 1040 7 7840 8 52864 9 327936 10 1912320 11 10644480 12 57164800 13 298428416 14 1522626560 15 7622451200 16 37551144960 17 182458122240 18 875972788224 19 4161315274752 20 19583780782080 21 91393766195200