# A258216 (b-file synthesized from sequence entry) 0 1 1 1 2 2 3 6 4 24 5 120 6 480 7 3600 8 30240 9 151200 10 1693440 11 20321280 12 121927680 13 1828915200 14 28740096000 15 201180672000 16 3793692672000 17 73977007104000 18 591816056832000 19 13463815292928000 20 314155690168320000