Conjecture on sums of rational approximations with prime denominators

Let α\alpha be a real number, let N1N\geq 1, let ϵ>0\epsilon>0, and let nϵlogNn\leq \epsilon\log N be a positive integer. Suppose that there are integers a,qa,q with 1qNn1\leq q\leq N^n and (a,q)=1(a,q)=1 such that

αa/q1/(qNn).|\alpha-a/q|\leq 1/(qN^n).

Sums of rational approximations conjecture. There are integers a1,,ana_1,\ldots,a_n and distinct primes q1,,qnq_1,\ldots,q_n with 1qiN1\leq q_i\leq N such that

αa1q1a2q2anqnϵ1qNnϵ.\left|\alpha-\frac{a_1}{q_1}-\frac{a_2}{q_2}-\cdots-\frac{a_n}{q_n}\right|\ll_\epsilon\frac{1}{qN^{n-\epsilon}}.

This conjecture predicts an essentially optimal preservation of the quality of a rational approximation while expressing the approximant as a sum with distinct prime denominators. The paper presents related partial results with a weaker exponent, but the supplied text does not establish the conjecture.

Sources & referencesView supporting material

Primary source

Tsz Ho Chan, “Approximating reals by sums of rationals”, arXiv:0704.2805 (2007).

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