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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.

A368624 a(n) = Sum_{k = 1..n} (-1)^(n+k) * gcd(2*k, n).

Table of values

n a(n)
1 1
2 0
3 3
4 4
5 5
6 0
7 7
8 16
9 9
10 0
11 11
12 20
13 13
14 0
15 15
16 48
17 17
18 0
19 19
20 36
21 21
22 0
23 23
24 80
25 25
26 0
27 27
28 52
29 29
30 0
31 31
32 128
33 33
34 0
35 35
36 84
37 37
38 0
39 39
40 144
41 41
42 0
43 43
44 84
45 45
46 0
47 47
48 240
49 49
50 0
51 51
52 100
53 53
54 0
55 55
56 208
57 57
58 0
59 59
60 180
61 61
62 0
63 63
64 320
65 65
66 0
67 67
68 132
69 69
70 0

List of values

[1, 0, 3, 4, 5, 0, 7, 16, 9, 0, 11, 20, 13, 0, 15, 48, 17, 0, 19, 36, 21, 0, 23, 80, 25, 0, 27, 52, 29, 0, 31, 128, 33, 0, 35, 84, 37, 0, 39, 144, 41, 0, 43, 84, 45, 0, 47, 240, 49, 0, 51, 100, 53, 0, 55, 208, 57, 0, 59, 180, 61, 0, 63, 320, 65, 0, 67, 132, 69, 0]

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

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