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A081047 as a simple table

na(n)
01
10
2-1
3-5
4-26
5-154
6-1044
7-8028
8-69264
9-663696
10-6999840
11-80627040
12-1007441280
13-13575738240
14-196287356160
15-3031488633600
16-49811492505600
17-867718162483200
18-15974614352793600
19-309920046408806400
20-6320046028584960000

[1,0,-1,-5,-26,-154,-1044,-8028,-69264,-663696,
 -6999840,-80627040,-1007441280,-13575738240,
 -196287356160,-3031488633600,-49811492505600,
 -867718162483200,-15974614352793600,
 -309920046408806400,-6320046028584960000]