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A012931 as a simple table

na(n)
00
12
2-1
3-12
442
5172
6-2250
7896
8153384
9-952688
10-11282040
11209648736
12279312528
13-43286799008
14318803909424
158375677890176
16-180484941598080
17-918969731775232
1879664942329607808
19-561407566293575168

[0,2,-1,-12,42,172,-2250,896,153384,-952688,
 -11282040,209648736,279312528,-43286799008,
 318803909424,8375677890176,-180484941598080,
 -918969731775232,79664942329607808,
 -561407566293575168]