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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.

A066180 a(n) = smallest base b so that repunit (b^prime(n) - 1) / (b - 1) is prime, where prime(n) = n-th prime; or 0 if no such base exists.

Table of values

n a(n)
1 2
2 2
3 2
4 2
5 5
6 2
7 2
8 2
9 10
10 6
11 2
12 61
13 14
14 15
15 5
16 24
17 19
18 2
19 46
20 3
21 11
22 22
23 41
24 2
25 12
26 22
27 3
28 2
29 12
30 86
31 2
32 7
33 13
34 11
35 5
36 29
37 56
38 30
39 44
40 60
41 304
42 5
43 74
44 118
45 33
46 156
47 46
48 183
49 72
50 606
51 602
52 223
53 115
54 37
55 52
56 104
57 41
58 6
59 338
60 217
61 13
62 136
63 220
64 162
65 35
66 10
67 218
68 19
69 26
70 39

List of values

[2, 2, 2, 2, 5, 2, 2, 2, 10, 6, 2, 61, 14, 15, 5, 24, 19, 2, 46, 3, 11, 22, 41, 2, 12, 22, 3, 2, 12, 86, 2, 7, 13, 11, 5, 29, 56, 30, 44, 60, 304, 5, 74, 118, 33, 156, 46, 183, 72, 606, 602, 223, 115, 37, 52, 104, 41, 6, 338, 217, 13, 136, 220, 162, 35, 10, 218, 19, 26, 39]

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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