KURSCHAK 1958 Problem 2

Show that if $m$ and $n$ are integers such that $m^2 + mn + n^2$ is divisible by $9$ , then they must both be divisible by $3$ .

Dataset text AI-MO AoPS. Quoted with source.

Solutions

No solution is on olymmath yet. Official and human solutions come first when they arrive. AI solutions come after them, with a label.