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A013161 as a simple table

na(n)
00
12
2-1
312
4-30
5270
6-1215
712600
8-81900
9992250
10-8434125
11117879300
12-1237732650
1319666196550
14-245827456875
154382752374000
16-63549909423000
171257302087291250
18-20745484440305625
19451231749105637500

[0,2,-1,12,-30,270,-1215,12600,-81900,992250,
 -8434125,117879300,-1237732650,19666196550,
 -245827456875,4382752374000,-63549909423000,
 1257302087291250,-20745484440305625,
 451231749105637500]