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A238087 as a simple table

na(n)
0-1
11
2-1
31
4-5
563
6-315
799
8-675675
9135135
10-1640925
1183329155
12-4583103525
135791834125
14-71152682225625
1514230536445125
16-26797763435625
1724833960277501375
18-73881031825566590625
198546099690638125
20-106610328924292590271875

[-1,1,-1,1,-5,63,-315,99,-675675,135135,-1640925,
 83329155,-4583103525,5791834125,-71152682225625,
 14230536445125,-26797763435625,24833960277501375,
 -73881031825566590625,8546099690638125,
 -106610328924292590271875]