# A204550 (b-file synthesized from sequence entry) 1 0 2 1 3 1 4 2 5 4 6 20 7 72 8 288 9 864 10 6624 11 35424 12 212544 13 1088640 14 10056960 15 75064320 16 600514560 17 4147200000 18 46664294400 19 440681472000 20 4406814720000 21 39103948800000 22 515545067520000