# A131446 (b-file synthesized from sequence entry) 1 1 2 1 3 1 4 8 5 15 6 720 7 5040 8 13440 9 13440 10 3628800 11 532224 12 43545600 13 691891200 14 691891200 15 108972864000 16 1902071808000 17 118562476032000 18 6847458508800 19 24329020081766400 20 17888985354240000 21 1344498478202880000