Question 123
How many ways are there to color every integer either red or blue such that $n$ and $n+7$ are the same color for all integers $n$, and there does not exist an integer $k$ such that $k$, $k+1$, and $2k$ are all the same color?
Math Olympiad Vault · MathNet 2022-part-06 — 196 problems (EN–VI)