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A038180
as a simple table
n
a(n)
1
1
2
2
3
6
4
44
5
394
6
4680
7
59361
8
789303
9
10742595
10
148921162
11
2093400002
12
29769338104
[1,2,6,44,394,4680,59361,789303,10742595, 148921162,2093400002,29769338104]