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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.

A278988 a(n) is the number of words of length n over an alphabet of size 3 that are in standard order and which have the property that every letter that appears in the word is repeated.

Table of values

n a(n)
0 0
1 0
2 1
3 1
4 4
5 11
6 41
7 162
8 610
9 2165
10 7327
11 23948
12 76352
13 239175
14 739909
15 2268710
16 6912430
17 20966441
18 63390587
19 191220048
20 575888044
21 1732382363
22 5207108161
23 15642295562
24 46970926394
25 141005053341
26 423208097431
27 1270026944852
28 3810919694680
29 11434503913775
30 34307135619197

List of values

[0, 0, 1, 1, 4, 11, 41, 162, 610, 2165, 7327, 23948, 76352, 239175, 739909, 2268710, 6912430, 20966441, 63390587, 191220048, 575888044, 1732382363, 5207108161, 15642295562, 46970926394, 141005053341, 423208097431, 1270026944852, 3810919694680, 11434503913775, 34307135619197]

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

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