cp's OEIS Frontend

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.

A307873 The concatenation pkp is the number obtained by placing prime p either side of R_k, the k-th repunit (1, k times); a(n) is the smallest k such that pkp is prime, where p=prime(n), or -1 if no such k exists.

Table of values

n a(n)
1 -1
2 1
3 -1
4 10905
5 15
6 2
7 1
8 2
9 3
10 1
11 3
12 173
13 1
14 14
15 1
16 43
17 1
18 5
19 11
20 1
21 2
22 3
23 3
24 1
25 2
26 -1
27 5
28 421
29 3
30 1
31 -1
32 1
33 1
34 3
35 -1
36 15
37 -1
38 3
39 3
40 163
41 -1
42 3
43 13
44 -1
45 679
46 -1
47 5
48 5
49 -1
50 107
51 93
52 1
53 -1
54 3
55 -1
56 1
57 -1
58 9
59 5
60 -1
61 -1
62 9
63 1089
64 -1
65 3
66 7
67 3
68 15
69 -1
70 27
71 -1
72 1
73 -1
74 27
75 17
76 25
77 1
78 15
79 3

List of values

[-1, 1, -1, 10905, 15, 2, 1, 2, 3, 1, 3, 173, 1, 14, 1, 43, 1, 5, 11, 1, 2, 3, 3, 1, 2, -1, 5, 421, 3, 1, -1, 1, 1, 3, -1, 15, -1, 3, 3, 163, -1, 3, 13, -1, 679, -1, 5, 5, -1, 107, 93, 1, -1, 3, -1, 1, -1, 9, 5, -1, -1, 9, 1089, -1, 3, 7, 3, 15, -1, 27, -1, 1, -1, 27, 17, 25, 1, 15, 3]