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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.

A117284 Numbers k for which the cototient k-phi(k) is a triangular number.

Table of values

n a(n)
1 1
2 2
3 3
4 5
5 7
6 9
7 10
8 11
9 13
10 17
11 19
12 23
13 29
14 31
15 37
16 39
17 41
18 43
19 45
20 47
21 52
22 53
23 54
24 55
25 57
26 59
27 61
28 67
29 68
30 71
31 73
32 79
33 83
34 85
35 89
36 90
37 97
38 101
39 103
40 107
41 109
42 113
43 114
44 117
45 127
46 129
47 131
48 137
49 139
50 149
51 151
52 157
53 159
54 163
55 167
56 168
57 173
58 175
59 179
60 181
61 191
62 193

List of values

[1, 2, 3, 5, 7, 9, 10, 11, 13, 17, 19, 23, 29, 31, 37, 39, 41, 43, 45, 47, 52, 53, 54, 55, 57, 59, 61, 67, 68, 71, 73, 79, 83, 85, 89, 90, 97, 101, 103, 107, 109, 113, 114, 117, 127, 129, 131, 137, 139, 149, 151, 157, 159, 163, 167, 168, 173, 175, 179, 181, 191, 193]

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

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