Abstract
Given a sequence (x n ) ∞n=1 of real numbers in the interval [0, 1) and a sequence (δ n ) ∞n=1 of positive numbers tending to zero, we consider the size of the set of numbers in [0, 1] which can be ‘well approximated’ by terms of the first sequence, namely, those y ∈ [0, 1] for which the inequality |y − x n | < δ n holds for infinitely many positive integers n. We show that the set of ‘well approximable’ points by a sequence (x n ) ∞n=1 , which is dense in [0, 1], is ‘quite large’ no matter how fast the sequence (δ n ) ∞n=1 converges to zero. On the other hand, for any sequence of positive numbers (δ n ) ∞n=1 tending to zero, there is a well distributed sequence (x n ) ∞n=1 in the interval [0, 1] such that the set of ‘well approximable’ points y is ‘quite small’.
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Berend, D., Dubickas, A. Good points for diophantine approximation. Proc Math Sci 119, 423–429 (2009). https://doi.org/10.1007/s12044-009-0040-1
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DOI: https://doi.org/10.1007/s12044-009-0040-1