Conjecture on rational approximations with prescribed numbers of prime divisors

Let α\alpha be a real number, let X1X\geq 1, let ϵ>0\epsilon>0, and let nϵlogXn\leq \epsilon\log X be a natural number. Suppose that there are integers a,qa,q with 1qX1\leq q\leq X and (a,q)=1(a,q)=1 such that

αa/q1/(qX).|\alpha-a/q|\leq 1/(qX).

Prescribed-prime-divisors conjecture. There is a rational number A/QA/Q such that QX1+ϵQ\leq X^{1+\epsilon}, ω(Q)=n\omega(Q)=n, and

αAQϵ1qX1ϵ.\left|\alpha-\frac{A}{Q}\right|\ll_\epsilon\frac{1}{qX^{1-\epsilon}}.

This asserts that a rational approximation can be replaced by one with a prescribed number of distinct prime divisors in its denominator, with only a small loss in the approximation exponent. The supplied text gives heuristic motivation and related corollaries, but no resolution.

Sources & referencesView supporting material

Primary source

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

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