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A030444
as a simple table
n
a(n)
1
1
2
4
3
28
4
234
5
2162
6
20972
7
209608
8
2135572
9
22049959
10
229939414
11
2416816416
12
25569786440
13
272057195864
[1,4,28,234,2162,20972,209608,2135572,22049959, 229939414,2416816416,25569786440,272057195864]