Maximal mm-palindromic density conjecture

Let mNm\in\mathbb{N}, and let ANN0A\in\mathbb{N}^{\mathbb{N}_0} be an mm-palindromic sequence that is not eventually periodic. Let dm([A])d_m([A]) denote its mm-palindromic density. For r,sNr,s\in\mathbb{N} with rsr\not=s, let F(m,r,s)F(m,r,s) be the sequence obtained from the Fibonacci sequence by replacing each occurrence of one symbol by (rm,r)(rm,r) and each occurrence of the other by (sm,s)(sm,s), and let φ\varphi be the golden ratio. Maximal mm-palindromic density conjecture. For every such AA, one has

dm([A])1φ.d_m([A])\leq\frac{1}{\varphi}.

Furthermore,

dm([F(m,r,s)])=1φ.d_m([F(m,r,s)])=\frac{1}{\varphi}.

This conjectures that the constructed sequences attain the maximal mm-palindromic density among non-eventually-periodic mm-palindromic sequences, extending the known m=1m=1 result for the Fibonacci word. The surrounding construction establishes the lower bound for these Fibonacci-derived sequences, while the asserted universal upper bound is the conjectural part.

Sources & referencesView supporting material

Primary source

David M. Freeman, “Generalized Palindromic Continued Fractions”, arXiv:1604.06755 (2017).

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