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Multicolour Triangle Ramsey Numbers (Erdős #183)

AI-resolved

Posed by Paul Erdős · 1970 · Ramsey theory · resolved 2026

The problem

Let \(R_{k}\)(3) be the least n such that any k-colouring of the edges of \(K_{n}\) yields a monochromatic triangle. Erdős asked how fast \(R_{k}\)(3) grows; the conjectured lower-bound mechanism (probabilistic) gave roughly c·k! growth. Erdős problem #183 asks for a superexponential construction.

History & significance

Ramsey numbers are notoriously resistant: even R(5,5) is unknown between 43 and 48. The multicolour triangle function was pinned between exponential and factorial bounds for decades, with improvements measured in constant factors.