A082640 - OEIS

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A082640 as a simple table

n	a(n)
1	2
2	6
3	64
4	20
5	852
6	46456
7	70
8	12170
9	2822648
10	736983568
11	252
12	182132
13	182881520
14	208902766788
15	260420548144996
16	924
17	2801708
18	12244184472
19	61756221742966
20	341816489625522032
21	1999206934751133055518

[2,6,64,20,852,46456,70,12170,2822648,736983568, 252,182132,182881520,208902766788,260420548144996, 924,2801708,12244184472,61756221742966, 341816489625522032,1999206934751133055518]