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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.

A270416 Numbers n such that sigma(n) - 1 and sigma(phi(n)) are both primes.

Table of values

n a(n)
1 3
2 5
3 6
4 10
5 17
6 34
7 40
8 60
9 85
10 136
11 204
12 240
13 4369
14 8224
15 8704
16 8738
17 10880
18 12336
19 13056
20 65537
21 131074
22 131584
23 139264
24 163840
25 164480
26 174760
27 208896
28 245760
29 262140
30 524296
31 526336
32 559232
33 835584
34 838848
35 2281736192
36 2694881440
37 2852170240
38 2863267840
39 3221274624
40 3233857728
41 4026593280

List of values

[3, 5, 6, 10, 17, 34, 40, 60, 85, 136, 204, 240, 4369, 8224, 8704, 8738, 10880, 12336, 13056, 65537, 131074, 131584, 139264, 163840, 164480, 174760, 208896, 245760, 262140, 524296, 526336, 559232, 835584, 838848, 2281736192, 2694881440, 2852170240, 2863267840, 3221274624, 3233857728, 4026593280]

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

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