# A089423 (b-file synthesized from sequence entry) 0 1 1 1 2 2 3 6 4 12 5 120 6 120 7 840 8 840 9 5040 10 5040 11 55440 12 55440 13 720720 14 720720 15 720720 16 720720 17 24504480 18 24504480 19 465585120 20 465585120