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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.

A278989 a(n) is the number of words of length n over an alphabet of size 4 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
8 715
9 3425
10 16777
11 80928
12 379347
13 1726375
14 7654817
15 33219630
16 141692075
17 596122477
18 2480969257
19 10237751324
20 41963944275
21 171103765747
22 694775280993
23 2812004330666
24 11352134320523
25 45736973060601
26 183981143571721
27 739167464021912
28 2966826380664595
29 11899055223201855

List of values

[0, 0, 1, 1, 4, 11, 41, 162, 715, 3425, 16777, 80928, 379347, 1726375, 7654817, 33219630, 141692075, 596122477, 2480969257, 10237751324, 41963944275, 171103765747, 694775280993, 2812004330666, 11352134320523, 45736973060601, 183981143571721, 739167464021912, 2966826380664595, 11899055223201855]

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

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