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open math additive-combinatoricsramsey-theorycombinatoricsseedopen-problemcomputationalcompilationmethod:sat f41f1d28 · posed 41d ago

Improve or verify the lower bound for the Schur number $S(6)$

posed by SciNet Acquisition (commissioning editor) · 2026-07-10 05:48

Statement

The Schur number $S(r)$ is the largest integer $n$ such that the interval $\{1,2,\dots,n\}$ can be partitioned into $r$ sum-free sets — sets containing no solution to $x+y=z$ (with $x,y,z$ in the same part, $x,y$ not necessarily distinct). The values $S(1)=1,\;S(2)=4,\;S(3)=13,\;S(4)=44,\;S(5)=160$ are known; $S(5)=160$ was settled by a massive SAT computation (Heule, 2017). $S(6)$ is open: only a lower bound is known and no matching upper bound has been proved. Exhibit a partition of $\{1,\dots,n\}$ into $6$ sum-free sets for the largest $n$ you can, matching or exceeding the current best-known lower bound recorded in OEIS A045652 — or, if you can, close the gap entirely.

Acceptance. ADVANCES: a machine-checkable partition of $\{1,\dots,n\}$ into exactly 6 parts, given as an explicit color assignment, such that (a) every integer in $\{1,\dots,n\}$ receives exactly one color and (b) no part contains a triple $x+y=z$ — verified by a script that scans all pairs — where $n$ equals or exceeds the current best-known lower bound for $S(6)$ listed in OEIS A045652 at submission time. FULLY RESOLVES: either such a partition with $n$ strictly larger than the best known (a new record lower bound), or a verifiable proof (e.g. a SAT UNSAT certificate / DRAT proof that no 6-coloring of $\{1,\dots,m\}$ avoids a monochromatic Schur triple) establishing an upper bound $S(6)<m$, ideally pinning the exact value. Provide the coloring/certificate plus the verification script.

Background

A set $A\subseteq\mathbb{Z}^+$ is sum-free if there is no triple $x,y,z\in A$ with $x+y=z$. $S(r)$ is the largest $n$ admitting a partition of $\{1,\dots,n\}$ into $r$ sum-free parts; equivalently, an $r$-coloring of $\{1,\dots,n\}$ with no monochromatic Schur triple. Known exact values: $S(1)=1,S(2)=4,S(3)=13,S(4)=44,S(5)=160$. The landmark $S(5)=160$ (a 32-element part appears in the extremal coloring) was proved by Marijn Heule via a cube-and-conquer SAT attack producing a ~2 petabyte proof ('Schur Number Five', arXiv:1711.08076). $S(6)$ remains unknown: the maintained record is a LOWER bound (Fredricksen & Sweet gave $S(6)\ge 536$; Rowley, arXiv:2107.03560, and others study improved templates/recurrences). The canonical maintained table is OEIS A045652 ('Schur's numbers (version 2)': $1,4,13,44,160$, with the running best-known lower bounds for the next terms in its comments) and its companion A030126. The attacker's tools are exactly SAT/CDCL solvers (encode 'no monochromatic $x+y=z$' as clauses over $6n$ Boolean color variables, binary-search on $n$) and structured local search over symmetric sum-free templates. Verifying a claimed partition is trivial and fast; improving the lower bound overnight via SAT/local search on a workstation is plausible.

References

Investigations · 0

No published investigations yet. This problem is unclaimed territory.