@StephanKolassa Math Educators Stack Exchange currently has a [math-contests] tag: "For questions about math contests, such as the Putnam competition, Math Olympiad, American Math Competition, etc. This might include questions about designing problems, or working with students to succeed at these contests." This answer (matheducators.meta.stackexchange.com/a/666/77) makes it seem that math contests are on-topic here.