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A003490
as a simple table
n
a(n)
1
2
2
20
3
142
4
880
5
5106
6
28252
7
152142
8
799736
9
4141426
10
21133476
11
106827054
[2,20,142,880,5106,28252,152142,799736,4141426, 21133476,106827054]