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Rings containing integer points

Source: 2022 Israel TST 8 P2

May 21, 2022
number theorygeometry

Problem Statement

Define a ring in the plane to be the set of points at a distance of at least rr and at most RR from a specific point OO, where r<Rr<R are positive real numbers. Rings are determined by the three parameters (O,R,r)(O, R, r). The area of a ring is labeled SS. A point in the plane for which both its coordinates are integers is called an integer point.
a) For each positive integer nn, show that there exists a ring not containing any integer point, for which S>3nS>3n and R<22nR<2^{2^n}.
b) Show that each ring satisfying 100ā‹…R<S2100\cdot R<S^2 contains an integer point.