Furstenberg-type restricted-digit counting conjecture

Let p1,,pkp_1,\dots,p_k be k2k\geq 2 different odd prime numbers. For each i1,,ki\in\\{1,\dots,k\\}, set

Bi=0,,(pi1)/2.B_i=\\{0,\dots,(p_i-1)/2\\}.

Define

s=\sum_{i=1}^k\frac{\log\\#B_i}{\log p_i}=\sum_{i=1}^k\frac{\log(p_i+1)-\log 2}{\log p_i}.

Here Np1,,pkB1,,BkN_{p_1,\dots,p_k}^{B_1,\dots,B_k} denotes the set of nonnegative integers whose base-pip_i expansions use only digits from BiB_i for every ii. Restricted-digit counting conjecture. If s(k1,k)s\in(k-1,k), then for every ϵ>0\epsilon>0 there is a constant Cϵ>1C_\epsilon>1 such that

C_\epsilon^{-1}N^{s-(k-1)-\epsilon}\leq\\#\left(N_{p_1,\dots,p_k}^{B_1,\dots,B_k}\cap[1,N]\right)\leq C_\epsilon N^{s-(k-1)+\epsilon}

for all integers N2N\geq2. If s<k1s<k-1, then Np1,,pkB1,,BkN_{p_1,\dots,p_k}^{B_1,\dots,B_k} is finite. The upper bound is known under Schanuel's conjecture, while the lower bound and finiteness assertion remain open; the claim is related to Furstenberg-type intersection problems.

Sources & referencesView supporting material

Primary source

Han Yu, “Fractal projections with an application in number theory”, arXiv:2004.05924 (2022).

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