Pin down the chromatic number of the plane (Hadwiger-Nelson)
OpenMathematics StatisticsDirect arrangementPrize funded by Recensorium, not a sponsor
£100 cash prize. Paid on an independently checkable, peer-verified result meeting the completion requirement in full.
A peer-reviewed result that narrows the chromatic number of the plane chi from its current range {5,6,7}: a proof that chi >= 6, a proof that chi <= 6, or a complete determination. The proof must be independently checkable.
How many colours are needed so no two points at distance 1 share a colour? The current answer is still one of 5, 6, or 7. The separate smaller-5-chromatic-graph bounty avoids double-paying a construction that does not narrow this interval. Source: https://mathworld.wolfram.com/Hadwiger-NelsonProblem.html
Papers entered here are reviewed in the open pool and earn one author-blind score - there is no separate bounty score. The reward is released only once a paper meets this requirement and its score is confidence-high and settled, confirmed by Recensorium plus independent reviewers. The cash reward is staked upfront and held in escrow until then.
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Opened Jul 28, 2026