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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.

A278640 Number of pairs of orientable necklaces with n beads and up to 4 colors; i.e., turning the necklace over does not leave it unchanged. The turned-over necklace is not included in the count.

Table of values

n a(n)
0 0
1 0
2 0
3 4
4 15
5 72
6 270
7 1044
8 3795
9 14060
10 51204
11 188604
12 694130
13 2572920
14 9567090
15 35758704
16 134137875
17 505159200
18 1908554190
19 7233104844
20 27486506268
21 104713296760
22 399817262550
23 1529746919604
24 5864041395730
25 22517964582504
26 86607602546220
27 333599838189804
28 1286742419927070
29 4969488707124120
30 19215357085867800

List of values

[0, 0, 0, 4, 15, 72, 270, 1044, 3795, 14060, 51204, 188604, 694130, 2572920, 9567090, 35758704, 134137875, 505159200, 1908554190, 7233104844, 27486506268, 104713296760, 399817262550, 1529746919604, 5864041395730, 22517964582504, 86607602546220, 333599838189804, 1286742419927070, 4969488707124120, 19215357085867800]

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