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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.

A351970 a(0) = 1; a(n) = Sum_{k=0..floor(n/3)} binomial(n,3*k) * a(k).

Table of values

n a(n)
0 1
1 1
2 1
3 2
4 5
5 11
6 22
7 43
8 85
9 171
10 351
11 738
12 1590
13 3498
14 7827
15 17757
16 40725
17 94113
18 218439
19 507852
20 1180395
21 2739312
22 6342084
23 14642100
24 33703182
25 77344686
26 176984406
27 403901722
28 919533655
29 2089000936
30 4737194867
31 10726221713
32 24257223605
33 54805216567

List of values

[1, 1, 1, 2, 5, 11, 22, 43, 85, 171, 351, 738, 1590, 3498, 7827, 17757, 40725, 94113, 218439, 507852, 1180395, 2739312, 6342084, 14642100, 33703182, 77344686, 176984406, 403901722, 919533655, 2089000936, 4737194867, 10726221713, 24257223605, 54805216567]

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