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A012251 as a simple table

na(n)
01
11
21
3-2
4-11
524
6349
7-720
8-22455
940320
102465241
11-3628800
12-416217603
13479001600
14100729124469
15-87178291200
16-33198564667887
1720922789888000
1814328891118054449
19-6402373705728000
20-7852649782447649403

[1,1,1,-2,-11,24,349,-720,-22455,40320,2465241,
 -3628800,-416217603,479001600,100729124469,
 -87178291200,-33198564667887,20922789888000,
 14328891118054449,-6402373705728000,
 -7852649782447649403]