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Find the maximum number c

Source: IMO Longlist 1989, Problem 109

September 18, 2008
algebra unsolvedalgebra

Problem Statement

Find the maximum number c c such that for all nNn \in \mathbb{N} to have {n2}cn \{n \cdot \sqrt{2}\} \geq \frac{c}{n} where \{n \cdot \sqrt{2}\} \equal{} n \cdot \sqrt{2} \minus{} [n \cdot \sqrt{2}] and [x] [x] is the integer part of x. x. Determine for this number c, c, all nN n \in \mathbb{N} for which \{n \cdot \sqrt{2}\} \equal{} \frac{c}{n}.