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arXiv 0801.4310math.NTmath.GM
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一种改进的无级数集构造法

An Improved Construction of Progression-Free Sets

Michael Elkin

摘要:

构造{1,2,.}的稠密子集S的问题,不包含算术三元组的n}是由Erdos和Turan在1936年提出的。他们给出了一个|S| = Ω(n^{ \log_3 2})元素的构造。它们的结构由塞勒姆和斯宾塞改进,并在1946年由贝伦德进一步改进。贝伦德的下界是|S| = Ω({n \over {2^{2 \sqrt{2} \sqrt{\log_2 n} } \cdot \log^{1/4} n}})。从那时起,这个问题就成为加性数论中最核心、最基本、研究最深入的问题之一。然而,自1946年以来,没有关于贝伦德下界的改进的报道。本文提出了一种构造方法,将Behrend的结果改进了一个因子Theta(\sqrt{\log n}),并证明了|S| = Omega({\over {2^{2 \sqrt{2} \sqrt{\log_2 n} } \cdot \log^{1/4} n).特别地,我们的结果意味着Behrend的构造不是最优的。我们的构造和证明是基本的和独立的。

英文摘要:

The problem of constructing dense subsets S of {1,2,..,n} that contain no arithmetic triple was introduced by Erdos and Turan in 1936. They have presented a construction with |S| = Ω(n^{\log_3 2}) elements. Their construction was improved by Salem and Spencer, and further improved by Behrend in 1946. The lower bound of Behrend is |S| = Omega({n \over {2^{2 \sqrt{2} \sqrt{\log_2 n}} \cdot \log^{1/4} n}}). Since then the problem became one of the most central, most fundamental, and most intensively studied problems in additive number theory. Nevertheless, no improvement of the lower bound of Behrend was reported since 1946. In this paper we present a construction that improves the result of Behrend by a factor of Theta(\sqrt{\log n}), and shows that |S| = Omega({n \over {2^{2 \sqrt{2} \sqrt{\log_2 n}}}} \cdot \log^{1/4} n). In particular, our result implies that the construction of Behrend is not optimal. Our construction and proof are elementary and self-contained.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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