English

On the size of the set A(A+1)

Number Theory 2008-12-16 v3

Abstract

Let FpF_p be the field of a prime order p.p. For a subset AFpA\subset F_p we consider the product set A(A+1).A(A+1). This set is an image of A×AA\times A under the polynomial mapping f(x,y)=xy+x:Fp×FpFp.f(x,y)=xy+x:F_p\times F_p\to F_p. In the present paper we show that if A<p1/2,|A|<p^{1/2}, then A(A+1)A106/105+o(1). |A(A+1)|\ge |A|^{106/105+o(1)}. If A>p2/3,|A|>p^{2/3}, then we prove that A(A+1)pA|A(A+1)|\gg \sqrt{p |A|} and show that this is the optimal in general settings bound up to the implied constant. We also estimate the cardinality of A(A+1)A(A+1) when AA is a subset of real numbers. We show that in this case one has the Elekes type bound A(A+1)A5/4. |A(A+1)|\gg |A|^{5/4}.

Keywords

Cite

@article{arxiv.0811.4206,
  title  = {On the size of the set A(A+1)},
  author = {M. Z. Garaev and Chun-Yen Shen},
  journal= {arXiv preprint arXiv:0811.4206},
  year   = {2008}
}

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