olymmath

ISL 2020 N6

For a positive integer nn, let d(n)d(n) be the number of positive divisors of nn, and let φ(n)\varphi(n) be the number of positive integers not exceeding nn which are coprime to nn. Does there exist a constant CC such that φ(d(n))d(φ(n))⩽C\frac{\varphi(d(n))}{d(\varphi(n))} \leqslant C for all n⩾1n \geqslant 1 ? (Cyprus)

Official text Transcription from NuminaMath olympiads, checked word for word against the official paper. Quoted with source.

Official text: IMO 2020 Shortlist booklet, page 12.

Solutions

Official solution Solution 1 by the IMO Problem Selection Committee

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