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A004990 as a simple table

na(n)
01
1-3
2-9
3-45
4-270
5-1782
6-12474
7-90882
8-681615
9-5225715
10-40760577
11-322379109
12-2579032872
13-20830650120
14-169621008120
15-1390892266584
16-11474861199318
17-95173848770814
18-793115406423450
19-6637123664280450
20-55751838779955780

[1,-3,-9,-45,-270,-1782,-12474,-90882,-681615,
 -5225715,-40760577,-322379109,-2579032872,
 -20830650120,-169621008120,-1390892266584,
 -11474861199318,-95173848770814,-793115406423450,
 -6637123664280450,-55751838779955780]