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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.

A139558 a(1)=4. For n>=2, a(n) = smallest integer > a(n-1) that is not coprime to (n+1) but is coprime to n.

Table of values

n a(n)
1 4
2 9
3 10
4 15
5 16
6 35
7 36
8 39
9 40
10 77
11 78
12 91
13 92
14 93
15 94
16 119
17 120
18 133
19 134
20 141
21 142
22 161
23 162
24 175
25 176
26 177
27 178
28 261
29 262
30 341
31 342
32 345
33 346
34 355
35 356
36 407
37 408
38 411
39 412
40 451
41 452
42 473
43 474
44 475
45 476
46 517
47 518
48 539
49 540
50 543
51 548
52 583
53 584
54 595
55 596
56 597

List of values

[4, 9, 10, 15, 16, 35, 36, 39, 40, 77, 78, 91, 92, 93, 94, 119, 120, 133, 134, 141, 142, 161, 162, 175, 176, 177, 178, 261, 262, 341, 342, 345, 346, 355, 356, 407, 408, 411, 412, 451, 452, 473, 474, 475, 476, 517, 518, 539, 540, 543, 548, 583, 584, 595, 596, 597]

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

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