Accumulation-point conjecture for quotient values of binary sequences

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Let u=(un)n∈N{\bf u}=(u_n)_{n\in\mathbb{N}} be a binary sequence that is not eventually periodic. Suppose that the set of return lengths R(u)\mathcal{R}(\mathbf{u}) is finite, and that

{n∈N:un=0, un+1=un+2=un+3=1}\{n\in\mathbb{N}: u_n=0,\ u_{n+1}=u_{n+2}=u_{n+3}=1\}

is infinite. Let ff be the sequence defined by the paper's equation for f(n)f(n), and let V(f)\mathcal{V}(f) denote its set of quotient values. Accumulation-point conjecture. For almost all pairs (a,b)(a,b) in the sense of asymptotic density, the set V(f)\mathcal{V}(f) has infinitely many accumulation points. More precisely, its set of accumulation points in R∪{∞}\mathbb{R}\cup\{\infty\} is homeomorphic either to a union of the Cantor set and a finite set or to the whole set R∪{∞}\mathbb{R}\cup\{\infty\}. The conjecture concerns the structure of quotient values generated by non-eventually-periodic binary sequences; the asserted almost-everywhere conclusion and the alternatives for the accumulation set remain unproved in the supplied text.

References

Primary source

Piotr Miska, Bartosz Sobolewski and Maciej Ulas, “Binary sequences meet the Fibonacci sequence”, arXiv:2412.11319 (2025).

Additional references

7 papers in this index state this conjecture (2001–2024). The statement above is taken from the most recent of them; the others are arXiv:2402.15369, arXiv:2001.08923, arXiv:1106.0017, arXiv:0805.0756, arXiv:0705.1210, arXiv:math/0104251.

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