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A015680 as a simple table

na(n)
01
1-1
23
3-15
481
5-585
64995
7-46935
8499905
9-6109425
1079791075
11-1138096575
1217774982225
13-294439570425
145240530570275
15-100050497922375
162002010508122625
17-42495475420022625
18954152290944727875

[1,-1,3,-15,81,-585,4995,-46935,499905,-6109425,
 79791075,-1138096575,17774982225,-294439570425,
 5240530570275,-100050497922375,2002010508122625,
 -42495475420022625,954152290944727875]