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A207018
as a simple table
n
a(n)
1
1
2
2
3
4
4
10
5
28
6
116
7
576
8
3634
9
26620
10
223440
11
2100964
12
21888712
13
250062982
14
3108430640
[1,2,4,10,28,116,576,3634,26620,223440,2100964, 21888712,250062982,3108430640]