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A000609
as a simple table
n
a(n)
0
2
1
4
2
14
3
104
4
1882
5
94572
6
15028134
7
8378070864
8
17561539552946
9
144130531453121108
[2,4,14,104,1882,94572,15028134,8378070864, 17561539552946,144130531453121108]