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A143881
as a simple table
n
a(n)
0
1
1
2
2
15
3
207
4
6084
5
292607
6
23511001
7
3132847224
8
693856861039
9
259806377729539
[1,2,15,207,6084,292607,23511001,3132847224, 693856861039,259806377729539]