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A074831
as a simple table
n
a(n)
1
3
2
20
3
101
4
508
5
3053
6
20053
7
141772
8
1045600
9
8038954
10
63830588
11
518935134
12
4311185894
[3,20,101,508,3053,20053,141772,1045600,8038954, 63830588,518935134,4311185894]