# A024420 (b-file synthesized from sequence entry)
0 1
1 1
2 1
3 4
4 22
5 108
6 612
7 4416
8 36576
9 331200
10 3319200
11 36806400
12 445046400
13 5813579520
14 81716947200
15 1230656716800
16 19761225523200
17 336973967769600
18 6082189179494400
19 115851849523200000
20 2322322137354240000
21 48869666136023040000