A009335 - OEIS

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A009335 as a simple table

n	a(n)
0	0
1	1
2	-1
3	4
4	-8
5	40
6	-121
7	768
8	-3128
9	24320
10	-124921
11	1152512
12	-7158128
13	76477440
14	-557749921
15	6773211136
16	-56767019408
17	772218880000
18	-7316056402321
19	110191426928640
20	-1164842760597368
21	19241219430809600

[0,1,-1,4,-8,40,-121,768,-3128,24320,-124921, 1152512,-7158128,76477440,-557749921,6773211136, -56767019408,772218880000,-7316056402321, 110191426928640,-1164842760597368, 19241219430809600]