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A006439
as a simple table
n
a(n)
1
4
2
152
3
2630
4
31500
5
303534
6
2530976
7
19030428
8
132386340
9
866782510
10
5405853200
[4,152,2630,31500,303534,2530976,19030428, 132386340,866782510,5405853200]