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A002686
as a simple table
n
a(n)
1
1
2
8
3
45
4
416
5
1685
6
31032
7
1603182
8
13856896
9
132843888
10
6551143600
[1,8,45,416,1685,31032,1603182,13856896,132843888, 6551143600]