# A090753 (b-file synthesized from sequence entry) 0 1 1 2 2 2 3 4 4 16 5 88 6 600 7 4800 8 43680 9 443296 10 4949920 11 60217408 12 792134528 13 11200176128 14 169375195136 15 2728019576832 16 46626359376384 17 842947307334144 18 16073131554826752 19 322403473258650624 20 6786861273524305920