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A001206
as a simple table
n
a(n)
0
0
1
1
2
2
3
4
4
12
5
81
6
2646
7
1422564
8
229809982112
9
423295099074735261880
[0,1,2,4,12,81,2646,1422564,229809982112, 423295099074735261880]