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A226891
as a simple table
n
a(n)
2
1
3
2
4
4
5
19
6
63
7
153
8
1273
9
2090
10
19227
11
266133
12
868868
13
10631543
14
264365332
15
662822809
16
129102309125
[1,2,4,19,63,153,1273,2090,19227,266133,868868, 10631543,264365332,662822809,129102309125]