# A002670 (b-file synthesized from sequence entry) 1 1 2 2 3 12 4 72 5 240 6 2400 7 907200 8 4233600 9 25401600 10 1371686400 11 251475840000 12 5532468480000 13 554827553280000 14 33659538232320000 15 73302994372608000 16 4453156908135936000000 17 50469111625540608000000 18 63553696121051136000000