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OlympiadBench / 1964 / Let Z_(>0) denote the set of positive integers. For any positive…

Problem

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question

Let Z>0\mathbb{Z}_{>0} denote the set of positive integers. For any positive integer kk, a function f:Z>0Z>0f: \mathbb{Z}_{>0} \rightarrow \mathbb{Z}_{>0} is called kk-good if gcd(f(m)+n,f(n)+m)k\operatorname{gcd}(f(m)+n, f(n)+m) \leqslant k for all mnm \neq n. Find all kk such that there exists a kk-good function.
Plain-text mathematical notation (without MathML)
Let Z_(>0) denote the set of positive integers. For any positive integer k, a function f:Z_(>0)→Z_(>0) is called k-good if gcd(f(m)+n,f(n)+m)≤k for all m≠n. Find all k such that there exists a k-good function.
Original LaTeX notation
Let $\mathbb{Z}_{>0}$ denote the set of positive integers. For any positive integer $k$, a function $f: \mathbb{Z}_{>0} \rightarrow \mathbb{Z}_{>0}$ is called $k$-good if $\operatorname{gcd}(f(m)+n, f(n)+m) \leqslant k$ for all $m \neq n$. Find all $k$ such that there exists a $k$-good function.

answer type

Expression

is multiple answer

false

language

English

question type

Open-ended

subject

Math

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