# A007657 (b-file synthesized from sequence entry)
1 1
2 2
3 6
4 36
5 270
6 2520
7 28560
8 361200
9 5481000
10 88565400
11 1654052400
12 32885455680
13 721400359680
14 17024709461760
15 429108154675200
16 11721695953968000
17 333806974560259200
18 10358856500289897600
19 331148326165228091520
20 11429645706428485536000
21 407641141014720316704000