# A003645 (b-file synthesized from sequence entry) 0 1 1 4 2 20 3 112 4 672 5 4224 6 27456 7 183040 8 1244672 9 8599552 10 60196864 11 426008576 12 3042918400 13 21909012480 14 158840340480 15 1158600130560 16 8496400957440 17 62605059686400 18 463277441679360 19 3441489566760960 20 25654740406763520 21 191852841302753280 22 1438896309770649600