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 A274018 Number of n-bead ternary necklaces (no turning over allowed) that avoid the subsequence 110. 5
 1, 3, 6, 10, 21, 42, 103, 237, 603, 1519, 3942, 10257, 27131, 71940, 192462, 516933, 1395636, 3781356, 10283911, 28050600, 76732047, 210414811, 578330649, 1592821005, 4395261552, 12149386569, 33637309323, 93267459520, 258961863288, 719938597227, 2003881480452, 5583818718102, 15575529493713 (list; graph; refs; listen; history; text; internal format)
 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 Table of n, a(n) for n=0..32. 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 Cf. A000031, A274017, A274019, A274020. Sequence in context: A061883 A027671 A167617 * A068149 A068709 A068804 Adjacent sequences: A274015 A274016 A274017 * A274019 A274020 A274021 KEYWORD nonn AUTHOR Marko Riedel, Jun 06 2016 STATUS approved

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Last modified August 13 21:23 EDT 2024. Contains 375144 sequences. (Running on oeis4.)