Problem 609

Erdős Problem #609: declared status 'open'. Formalized: no. Let $f(n)$ be the minimal $m$ such that if the edges of $K_{2^n+1}$ are coloured with $n$ colours then there must be a monochromatic odd cycle of length at most $m$. Estimate $f(n)$. Current best: The trivial upper bound is $2^n$. Prize: no. Tags: graph theory, ramsey theory.