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A009640 as a simple table

na(n)
00
11
2-1
32
4-10
546
6-226
71532
8-11880
996136
10-882376
119179312
12-102310000
131223945776
14-15941391376
15222827194592
16-3303846357120
1752077034777216
18-871329939918976
1915375474411183872
20-285315305595562240
215562663216718387456
22-113653337185088018176

[0,1,-1,2,-10,46,-226,1532,-11880,96136,-882376,
 9179312,-102310000,1223945776,-15941391376,
 222827194592,-3303846357120,52077034777216,
 -871329939918976,15375474411183872,
 -285315305595562240,5562663216718387456,
 -113653337185088018176]