cp's OEIS Frontend

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.

A335021 a(n) = Sum_{d|n, 1 < d < n} (-1)^(d + 1).

Table of values

n a(n)
1 0
2 0
3 0
4 -1
5 0
6 0
7 0
8 -2
9 1
10 0
11 0
12 -2
13 0
14 0
15 2
16 -3
17 0
18 0
19 0
20 -2
21 2
22 0
23 0
24 -4
25 1
26 0
27 2
28 -2
29 0
30 0
31 0
32 -4
33 2
34 0
35 2
36 -3
37 0
38 0
39 2
40 -4
41 0
42 0
43 0
44 -2
45 4
46 0
47 0
48 -6
49 1
50 0
51 2
52 -2
53 0
54 0
55 2
56 -4
57 2
58 0
59 0
60 -4
61 0
62 0
63 4
64 -5
65 2
66 0
67 0
68 -2
69 2
70 0
71 0
72 -6
73 0
74 0
75 4
76 -2
77 2
78 0
79 0
80 -6
81 3
82 0
83 0
84 -4
85 2
86 0
87 2
88 -4

List of values

[0, 0, 0, -1, 0, 0, 0, -2, 1, 0, 0, -2, 0, 0, 2, -3, 0, 0, 0, -2, 2, 0, 0, -4, 1, 0, 2, -2, 0, 0, 0, -4, 2, 0, 2, -3, 0, 0, 2, -4, 0, 0, 0, -2, 4, 0, 0, -6, 1, 0, 2, -2, 0, 0, 2, -4, 2, 0, 0, -4, 0, 0, 4, -5, 2, 0, 0, -2, 2, 0, 0, -6, 0, 0, 4, -2, 2, 0, 0, -6, 3, 0, 0, -4, 2, 0, 2, -4]