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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.

A180639 a(n) is the number of integers k <= n that are not solution of phi(x) = k for any x, where phi is the Euler totient function A000010.

Table of values

n a(n)
1 0
2 0
3 1
4 1
5 2
6 2
7 3
8 3
9 4
10 4
11 5
12 5
13 6
14 7
15 8
16 8
17 9
18 9
19 10
20 10
21 11
22 11
23 12
24 12
25 13
26 14
27 15
28 15
29 16
30 16
31 17
32 17
33 18
34 19
35 20
36 20
37 21
38 22
39 23
40 23
41 24
42 24
43 25
44 25
45 26
46 26
47 27
48 27
49 28
50 29
51 30
52 30
53 31
54 31
55 32
56 32
57 33
58 33
59 34
60 34
61 35
62 36
63 37
64 37
65 38
66 38
67 39
68 40
69 41
70 41

List of values

[0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 7, 8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 13, 14, 15, 15, 16, 16, 17, 17, 18, 19, 20, 20, 21, 22, 23, 23, 24, 24, 25, 25, 26, 26, 27, 27, 28, 29, 30, 30, 31, 31, 32, 32, 33, 33, 34, 34, 35, 36, 37, 37, 38, 38, 39, 40, 41, 41]

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

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