Normality of different orders for Cantor series expansions

Let S⊆N have the property that for each k∈S the set (S−k)∩N\S has asymptotic density 0. We prove that there exists a basic sequence Q where the set of numbers Q-normal of all orders in S but not Q-normal of all orders not in S has full Hausdorff dimension. If the function k↦1S(k) is computable, then...

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Veröffentlicht in:Nonlinearity 2017-10, Vol.30 (10), p.3719-3742, Article 3719
Hauptverfasser: Airey, Dylan, Mance, Bill
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Sprache:eng
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Zusammenfassung:Let S⊆N have the property that for each k∈S the set (S−k)∩N\S has asymptotic density 0. We prove that there exists a basic sequence Q where the set of numbers Q-normal of all orders in S but not Q-normal of all orders not in S has full Hausdorff dimension. If the function k↦1S(k) is computable, then there exist computable examples. For example, there exists a computable basic sequence Q where the set of numbers normal of all even orders and not normal of all odd orders has full Hausdorff dimension. This is in strong constrast to the b-ary expansions where any real number that is normal of order k must also be normal of all orders between 1 and k−1. Additionally, all numbers we construct satisfy the unusual condition that block frequencies sampled along non-trivial arithmetic progressions do not converge to the expected value. This is also in strong contrast to the case of the b-ary expansions, but more similar to the case of the continued fraction expansion. As a corollary, the set of Q-normal numbers that are not normal when sampled along any non-trivial arithmetic progression has full Hausdorff dimension.
ISSN:0951-7715
1361-6544
DOI:10.1088/1361-6544/aa82f0