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A013222 as a simple table

na(n)
00
10
2-1
31
4-6
515
6-105
7390
8-3500
915785
10-181125
11807750
12-12261150
1325793625
14-784508725
15-9327500000
1654587949000
17-5375441316375
1869535091676375
19-2529291250424250
2040837337931958750
21-1268829193109066875

[0,0,-1,1,-6,15,-105,390,-3500,15785,-181125,
 807750,-12261150,25793625,-784508725,-9327500000,
 54587949000,-5375441316375,69535091676375,
 -2529291250424250,40837337931958750,
 -1268829193109066875]