# A375796 (b-file synthesized from sequence entry) 0 1 1 1 2 2 3 6 4 36 5 240 6 1800 7 15960 8 164640 9 1905120 10 24343200 11 342619200 12 5269017600 13 87749101440 14 1573083832320 15 30218175187200 16 619256461824000 17 13483023576422400 18 310821905134540800 19 7563477205380096000 20 193736838233562624000 21 5210638309494858240000