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A009940 as a simple table

na(n)
01
10
2-1
3-4
4-15
5-56
6-185
7-204
86209
9112400
101520271
1119165420
12237686449
132944654296
1436392001815
15441823808804
165066513855745
1749021548330016
18202510138910239
19-8592616658156580
20-399625593156546319

[1,0,-1,-4,-15,-56,-185,-204,6209,112400,1520271,
 19165420,237686449,2944654296,36392001815,
 441823808804,5066513855745,49021548330016,
 202510138910239,-8592616658156580,
 -399625593156546319]