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A261005
as a simple table
n
a(n)
0
1
1
1
2
2
3
5
4
20
5
180
6
16143
7
489996795
8
1392195548399980210
9
789204635842035039135545297410259322
[1,1,2,5,20,180,16143,489996795, 1392195548399980210, 789204635842035039135545297410259322]