# 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