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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.

A209870 Numbers n for which tau(n) = tau(n'), where tau is the number of divisors of n and n' the arithmetic derivative of n.

Table of values

n a(n)
1 4
2 15
3 21
4 26
5 27
6 28
7 33
8 38
9 48
10 50
11 57
12 62
13 69
14 72
15 74
16 80
17 85
18 93
19 99
20 106
21 129
22 133
23 134
24 145
25 156
26 166
27 176
28 177
29 178
30 200
31 205
32 207
33 213
34 217
35 218
36 226
37 237
38 249
39 253
40 254
41 262
42 265
43 276
44 278
45 308
46 309
47 314
48 348
49 362
50 364
51 368
52 380
53 393
54 398
55 410
56 417

List of values

[4, 15, 21, 26, 27, 28, 33, 38, 48, 50, 57, 62, 69, 72, 74, 80, 85, 93, 99, 106, 129, 133, 134, 145, 156, 166, 176, 177, 178, 200, 205, 207, 213, 217, 218, 226, 237, 249, 253, 254, 262, 265, 276, 278, 308, 309, 314, 348, 362, 364, 368, 380, 393, 398, 410, 417]

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

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