2017 IMO Shortlist N8

Let $p$ be an odd prime number and $\mathbb{Z}_{>0}$ be the set of positive integers. Suppose that a function $f: \mathbb{Z}_{>0} \times \mathbb{Z}_{>0} \rightarrow\{0,1\}$ satisfies the following properties: - $f(1,1)=0$; - $f(a, b)+f(b, a)=1$ for any pair of relatively prime positive integers $(a, b)$ not both equal to 1 ; - $f(a+b, b)=f(a, b)$ for any pair of relatively prime positive integers $(a, b)$. Prove that $$\sum_{n=1}^{p-1} f\left(n^{2}, p\right) \geq \sqrt{2 p}-2$$

设$p$为奇素数，$\mathbb{Z}_{>0}$为正整数集合。假设函数 $f: \mathbb{Z}_{>0} \times \mathbb{Z}_{>0} \rightarrow\{0,1\}$ 满足以下属性： - $f(1,1)=0$； - $f(a, b)+f(b, a)=1$ 对于任何一对互素正整数 $(a, b)$ 且不均等于 1 ； - $f(a+b, b)=f(a, b)$ 对于任何一对互素正整数 $(a, b)$。证明 $$\sum_{n=1}^{p-1} f\left(n^{2}, p\right) \geq \sqrt{2 p}-2$$