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A003212
as a simple table
n
a(n)
0
1
1
4
2
12
3
36
4
108
5
264
6
708
7
1668
8
4536
9
10926
10
28416
11
67824
12
172464
13
408484
14
1035932
[1,4,12,36,108,264,708,1668,4536,10926,28416, 67824,172464,408484,1035932]