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A290331
as a simple table
n
a(n)
1
0
2
0
3
3
4
18
5
87
6
423
7
2340
8
15855
9
137160
10
1544121
11
22771791
12
443447013
[0,0,3,18,87,423,2340,15855,137160,1544121, 22771791,443447013]