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A013228 as a simple table

na(n)
00
10
2-1
31
4-6
515
6-105
7390
8-3500
915785
10-188685
11946350
12-15864750
1390057825
14-2127610485
1515254857800
16-444774915000
174213468013625
18-130378398500025
191538133793366950
20-48054409884965250

[0,0,-1,1,-6,15,-105,390,-3500,15785,-188685,
 946350,-15864750,90057825,-2127610485,15254857800,
 -444774915000,4213468013625,-130378398500025,
 1538133793366950,-48054409884965250]