# A110376 (b-file synthesized from sequence entry) 1 1 2 2 3 9 4 32 5 250 6 864 7 12348 8 67584 9 804816 10 5760000 11 116915040 12 686776320 13 19323757440 14 157991178240 15 2951575200000 16 42301705420800 17 1202482800691200 18 10048607738265600 19 425162773111910400 20 4541227794432000000