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A283021
as a simple table
n
a(n)
0
0
1
2
2
4
3
6
4
12
5
30
6
70
7
168
8
412
9
1014
10
2514
11
6270
12
15702
13
39468
14
99516
15
251586
16
637500
[0,2,4,6,12,30,70,168,412,1014,2514,6270,15702, 39468,99516,251586,637500]