MathNet 2017-part-02 — 176 problems (EN–VI) Question 25

What is the maximum number of elements that a subset of $\{1, 2, 3, \dots, 2017\}$ can have so that for any two distinct elements $a$ and $b$ of that subset, the number $a + b$ is not divisible by $a - b$? (Hong Kong 1992)