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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.

A307989 a(n) = n - pi(2*n) + pi(n-1), where pi is the prime counting function.

Table of values

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

List of values

[0, 0, 1, 2, 3, 4, 4, 6, 6, 6, 7, 8, 9, 11, 11, 11, 12, 14, 14, 16, 16, 16, 17, 18, 19, 20, 20, 21, 22, 23, 23, 25, 26, 26, 27, 27, 27, 29, 30, 30, 31, 32, 33, 35, 35, 36, 37, 39, 39, 40, 40, 40, 41, 42, 42, 43, 43, 44, 45, 47, 48, 50, 51, 51, 52, 52, 53, 55]

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

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