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A007206 as a simple table

na(n)
01
10
20
3-2
4-6
5-18
6-54
7-168
8-534
9-1732
10-5706
11-19038
12-64176
13-218190
14-747180
15-2574488
16-8918070
17-31036560
18-108457488
19-380390574
20-1338495492
21-4723664566
22-16714545822
23-59286878556
24-210755970528
25-750721297056
26-2679075662922
27-9577156141654
28-34290858526926
29-122959225609518

[1,0,0,-2,-6,-18,-54,-168,-534,-1732,-5706,-19038,
 -64176,-218190,-747180,-2574488,-8918070,
 -31036560,-108457488,-380390574,-1338495492,
 -4723664566,-16714545822,-59286878556,
 -210755970528,-750721297056,-2679075662922,
 -9577156141654,-34290858526926,-122959225609518]