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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.

A378681 a(n) = denominator(Sum_{k=1..n} 1/P_2(k)), where P_2(k) = A087040(k) is the second largest prime dividing the k-th composite number.

Table of values

n a(n)
1 2
2 1
3 2
4 6
5 3
6 6
7 3
8 3
9 6
10 2
11 1
12 3
13 6
14 3
15 15
16 30
17 30
18 15
19 5
20 10
21 30
22 15
23 15
24 15
25 30
26 10
27 5
28 15
29 30
30 30
31 15
32 30
33 210
34 210
35 70
36 35
37 105
38 105
39 210
40 210
41 105
42 35
43 70
44 210
45 105
46 21
47 21
48 42
49 14
50 70
51 210
52 105
53 105
54 210
55 210
56 210
57 105
58 35
59 70
60 210
61 210
62 105
63 105
64 210

List of values

[2, 1, 2, 6, 3, 6, 3, 3, 6, 2, 1, 3, 6, 3, 15, 30, 30, 15, 5, 10, 30, 15, 15, 15, 30, 10, 5, 15, 30, 30, 15, 30, 210, 210, 70, 35, 105, 105, 210, 210, 105, 35, 70, 210, 105, 21, 21, 42, 14, 70, 210, 105, 105, 210, 210, 210, 105, 35, 70, 210, 210, 105, 105, 210]

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

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