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A306551
as a simple table
n
a(n)
0
1
1
1
2
2
3
5
4
15
5
52
6
202
7
863
8
3999
9
19880
10
105134
11
587479
12
3449505
[1,1,2,5,15,52,202,863,3999,19880,105134,587479, 3449505]