# A052636 (b-file synthesized from sequence entry) 0 2 1 1 2 6 3 6 4 120 5 120 6 6480 7 5040 8 685440 9 362880 10 119750400 11 39916800 12 31135104000 13 6227020800 14 11245999564800 15 1307674368000 16 5377157001216000 17 355687428096000 18 3284417711038464000