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A002928 as a simple table

na(n)
01
10
2-2
3-8
4-34
5-152
6-714
7-3472
8-17318
9-88048
10-454378
11-2373048
12-12515634
13-66551016
14-356345666
15-1919453984
16-10392792766
17-56527200992
18-308691183938
19-1691769619240
20-9301374102034

[1,0,-2,-8,-34,-152,-714,-3472,-17318,-88048,
 -454378,-2373048,-12515634,-66551016,-356345666,
 -1919453984,-10392792766,-56527200992,
 -308691183938,-1691769619240,-9301374102034]