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A047871
as a simple table
n
a(n)
0
1
1
2
2
4
3
7
4
17
5
54
6
358
7
1859
8
13911
9
175164
10
3480256
11
97050825
12
1947896985
13
60119287462
[1,2,4,7,17,54,358,1859,13911,175164,3480256, 97050825,1947896985,60119287462]