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A006262
as a simple table
n
a(n)
1
1
2
2
3
18
4
4608
5
1800000000
6
5077997833420800000000
7
5608281336980602120684110607059901336780800000000
[1,2,18,4608,1800000000,5077997833420800000000, 5608281336980602120684110607059901336780800000000]