# A094253 (b-file synthesized from sequence entry) 1 1 2 8 3 20 4 120 5 496 6 2304 7 10240 8 46208 9 207360 10 932352 11 4189184 12 18827264 13 84606976 14 380223488 15 1708703744 16 7678853120 17 34508439552 18 155079540736 19 696921096192 20 3131935031296 21 14074788184064 22 63251524091904