# A227467 (b-file synthesized from sequence entry) 0 1 1 1 2 4 3 24 4 252 5 3660 6 73560 7 1921080 8 63411600 9 2574406800 10 125747475840 11 7258472907840 12 487590023511360 13 37629962101892160 14 3299990581104497280 15 325758967714868688000 16 35904380354917794720000 17 4387164775718671231084800 18 590610815931660911894707200 19 87118296156852814044256665600