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This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A373201 a(n) = smallest number m > 0 such that n followed by m 9's yields a prime, or -1 if no such m exists.

Table of values

n a(n)
1 1
2 1
3 -1
4 2
5 1
6 -1
7 1
8 1
9 -1
10 1
11 5
12 -1
13 1
14 1
15 -1
16 2
17 1
18 -1
19 1
20 2
21 -1
22 1
23 1
24 -1
25 3
26 1
27 -1
28 4
29 2
30 -1
31 28
32 2
33 -1
34 1
35 1
36 -1
37 1
38 1
39 -1
40 1
41 1
42 -1
43 1
44 1
45 -1
46 16
47 1
48 -1
49 1
50 1
51 -1
52 3
53 2
54 -1
55 5
56 1
57 -1
58 15
59 1
60 -1
61 1
62 2
63 -1
64 12
65 1
66 -1
67 4
68 2
69 -1
70 1
71 1
72 -1
73 1
74 2
75 -1
76 1
77 3

List of values

[1, 1, -1, 2, 1, -1, 1, 1, -1, 1, 5, -1, 1, 1, -1, 2, 1, -1, 1, 2, -1, 1, 1, -1, 3, 1, -1, 4, 2, -1, 28, 2, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 16, 1, -1, 1, 1, -1, 3, 2, -1, 5, 1, -1, 15, 1, -1, 1, 2, -1, 12, 1, -1, 4, 2, -1, 1, 1, -1, 1, 2, -1, 1, 3]