Erdős Problem 486: Logarithmic density for sets avoiding modular subsets #
For each $n \in \mathbb{N}$ choose some $X_n \subseteq \mathbb{Z}/n\mathbb{Z}$. Let $B = \{m \in \mathbb{N} : \forall n, m \not\equiv x \pmod{n} \text{ for all } x \in X_n\}$. Must $B$ have a logarithmic density?
Reference: erdosproblems.com/486
Erdős Problem 486
For each $n \in \mathbb{N}$ choose some $X_n \subseteq \mathbb{Z}/n\mathbb{Z}$. Let $B = \{m \in \mathbb{N} : \forall n, m \not\equiv x \pmod{n} \text{ for all } x \in X_n\}$. Must $B$ have a logarithmic density?