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A136591 as a simple table

na(n)
11
21
3-4
46
524
6-240
7720
85040
9-80640
10362880
113628800
12-79833600
13479001600
146227020800
15-174356582400
161307674368000
1720922789888000
18-711374856192000
196402373705728000
20121645100408832000
21-4865804016353280000
2251090942171709440000

[1,1,-4,6,24,-240,720,5040,-80640,362880,3628800,
 -79833600,479001600,6227020800,-174356582400,
 1307674368000,20922789888000,-711374856192000,
 6402373705728000,121645100408832000,
 -4865804016353280000,51090942171709440000]