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Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

A002019 as a simple table

na(n)
01
11
21
3-1
4-7
55
6145
7-5
8-6095
9-5815
10433025
11956375
12-46676375
13-172917875
147108596625
1538579649875
16-1454225641375
17-10713341611375
18384836032842625
193663118565923375
20-127950804666254375
21-1519935859717136875

[1,1,1,-1,-7,5,145,-5,-6095,-5815,433025,956375,
 -46676375,-172917875,7108596625,38579649875,
 -1454225641375,-10713341611375,384836032842625,
 3663118565923375,-127950804666254375,
 -1519935859717136875]