# A009681 (b-file synthesized from sequence entry)
0 0
1 1
2 2
3 6
4 16
5 72
6 288
7 1904
8 10368
9 89344
10 610304
11 6445824
12 52885504
13 660602880
14 6324756480
15 91175548928
16 997700468736
17 16301080281088
18 200677417680896
19 3664597991424000
20 50126593037172736
21 1011727950085619712