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A051459
as a simple table
n
a(n)
0
1
1
1
2
2
3
36
4
414720
5
189621927936000000
6
2156695499113014719143826715127578624000000000000
[1,1,2,36,414720,189621927936000000, 2156695499113014719143826715127578624000000000000]