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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.

A280057 a(n) = (-1)^n * 4*n/3 if n = 3*k and n!=0, otherwise a(n) = (-1)^n * n except a(0) = 1.

Table of values

n a(n)
0 1
1 -1
2 2
3 -4
4 4
5 -5
6 8
7 -7
8 8
9 -12
10 10
11 -11
12 16
13 -13
14 14
15 -20
16 16
17 -17
18 24
19 -19
20 20
21 -28
22 22
23 -23
24 32
25 -25
26 26
27 -36
28 28
29 -29
30 40
31 -31
32 32
33 -44
34 34
35 -35
36 48
37 -37
38 38
39 -52
40 40
41 -41
42 56
43 -43
44 44
45 -60
46 46
47 -47
48 64
49 -49
50 50
51 -68
52 52
53 -53
54 72
55 -55
56 56
57 -76
58 58
59 -59

List of values

[1, -1, 2, -4, 4, -5, 8, -7, 8, -12, 10, -11, 16, -13, 14, -20, 16, -17, 24, -19, 20, -28, 22, -23, 32, -25, 26, -36, 28, -29, 40, -31, 32, -44, 34, -35, 48, -37, 38, -52, 40, -41, 56, -43, 44, -60, 46, -47, 64, -49, 50, -68, 52, -53, 72, -55, 56, -76, 58, -59]

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