OFFSET
0,2
COMMENTS
The pattern in this enumeration must be contiguous (all three values next to each other in one sequence of three letters).
LINKS
Math Stackexchange, Marko Riedel et al., Counting circular sequences.
Marko Riedel, Maple code for this sequence.
FORMULA
G.f.: 1 - Sum_{n>=1} (phi(n)/n)*log(x^(3*n) - q*x^n + 1), where q=3 is the number of symbols in the alphabet we are using. - Petros Hadjicostas, Sep 12 2017
a(n) = (1/n)*Sum_{d|n} phi(n/d)*A215885(d) for n >= 1. - Petros Hadjicostas, Sep 13 2017
EXAMPLE
The necklace
1--1
/ \
0 0
| |
1 2
\ /
0--0
contains one instance of the subsequence starting in the upper left corner. Unlike a bracelet, the necklace is oriented.
CROSSREFS
KEYWORD
nonn
AUTHOR
Marko Riedel, Jun 06 2016
STATUS
approved