, 2022

Sets $X\subset \mathbb{Z}^{+}$ and $Y\subset \mathbb{Z}^{+}$ are called comradely, if every positive integer $n$ can be written as $n=xy$ for some $x\in X$ and $y\in Y$. Let $X(n)$ and $Y(n)$ denote the number of elements of $X$ and $Y$, respectively, among the first $n$ positive integers.