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A251808
as a simple table
n
a(n)
1
1
2
21
3
63
4
291
5
2744
6
2991
7
6102
8
6711
9
46676013
10
69460293
11
272543398
12
896172631
[1,21,63,291,2744,2991,6102,6711,46676013, 69460293,272543398,896172631]