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A006415
as a simple table
n
a(n)
0
4
1
104
2
1020
3
6092
4
26670
5
94128
6
283338
7
754380
8
1821534
9
4061200
[4,104,1020,6092,26670,94128,283338,754380, 1821534,4061200]