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A247054
as a simple table
n
a(n)
0
1
1
1
2
4
3
21
4
148
5
1305
6
13806
7
169681
8
2357560
9
36407241
10
621268930
[1,1,4,21,148,1305,13806,169681,2357560,36407241, 621268930]