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A076721 as a simple table

na(n)
10
2-1
3-1
41
5-1
624
7-1
849
914
1082
11-1
121700
13-1
14172
15201
16993
17-1
185793
19-1
207958
21409
22448
23-1
24331716
2594
26634
27689
2821896
29-1
30809928
31-1
3232705
331041
341102
351177
3610077605
37-1
381384
391465
402559910
41-1
423111600
43-1
4485100
4591047
462044
47-1
48254803844
49286
50124907

[0,-1,-1,1,-1,24,-1,49,14,82,-1,1700,-1,172,201,
 993,-1,5793,-1,7958,409,448,-1,331716,94,634,689,
 21896,-1,809928,-1,32705,1041,1102,1177,10077605,
 -1,1384,1465,2559910,-1,3111600,-1,85100,91047,
 2044,-1,254803844,286,124907]