W(2;3,21) = 416 - a van der Waerden number conjectured by Kullmann in 2010, now proved with a Lean 4 kernel-checked proof [R]

w(2;3,21) = 416 - today proved with a Lean 4 kernel- checked proof (preprint + 13.6 GB evidence package). Every red-blue colouring of {1, ..., 416} contains a red 3-term or a blue 21-term arithmetic progression, and some colouring of {1, ..., 415} contains neither. Kullmann conjectured the value in…

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1. 2026-10-29 20:46 · r/MachineLearning
   W(2;3,21) = 416 - a van der Waerden number conjectured by Kullmann in 2010, now proved with a Lean 4 kernel-checked proof [R]