# A121355 (b-file synthesized from sequence entry) 1 1 2 1 3 8 4 48 5 120 6 2640 7 30240 8 201600 9 4838400 10 96163200 11 1037836800 12 30496435200 13 828193766400 14 13686991718400 15 450537408921600 16 15880397524992000 17 356398802952192000 18 13410127414075392000 19 569542360114151424000 20 16614774394239909888000