Schur number S(6): 6 sum-free parts covering {1,...,N}

Recompute independently with scripts/audit-schur-6.mjs (Node, zero dependencies):
      node scripts/audit-schur-6.mjs <artifact-file>
    It parses either the JSON {"n":6,"parts":[[...],...]} form or the canonical digit-string
    form, checks that every integer 1..N appears in EXACTLY one of the 6 parts (both "missing"
    and "duplicate" are failures), then for each part scans all pairs x<=y within it (an O(size^2)
    scan per part, trivial even at N in the low thousands) to confirm x+y is never also in that
    part. It prints part sizes, PASS/FAIL, and on failure the exact violating triple (x, y, z) and
    part index. A dishonest or broken submission typically looks like one of: (a) an integer
    silently omitted from every part (so it never gets checked against anything, and the
    "partition" secretly covers only N-1 or fewer integers while claiming N); (b) an integer
    placed in two parts at once (inflates apparent coverage without cost); (c) a part that LOOKS
    sum-free because the checker only scanned x<y and missed x=y (e.g. a part containing 4 and 8,
    where 4+4=8 is a genuine violation even though there is only one copy of 4); (d) truncating a
    long digit-string submission so the tail integers are simply missing.

Background

The Schur number S(n) is the largest N such that {1,...,N} can be partitioned into n
"sum-free" parts, where a set is sum-free if it contains no x, y, z (x and y need not be
distinct, so x=y is allowed) with x + y = z. Issai Schur introduced this in 1916 in
connection with Fermat's Last Theorem mod p. S(1)=1, S(2)=4, and S(3)=13 are small enough to
verify by hand or brute force; S(4)=44 was established by Golomb and Baumert in 1965 (also
reachable by computer search). S(5)=160 was a genuinely hard open problem for decades: a
5-coloring of {1,...,160} achieving it was known (G. Exoo, 1994), but proving no larger N was
possible required Marijn Heule's 2017 tour de force, "Schur Number Five" (arXiv:1711.08076,
also AAAI 2018): a massively parallel SAT computation (cube-and-conquer, millions of
subproblems) producing a proof of unsatisfiability for N=161 that is, in compressed form,
over 2 petabytes, independently certified with the ACL2 theorem prover.

S(6) is OPEN: nobody knows its exact value. The best known lower bound is S(6) >= 536, due
to H. Fredricksen and M. M. Sweet, "A Lower Bound for Schur Numbers and Multicolor Ramsey
Numbers of K_3", Electronic Journal of Combinatorics (2000) -- i.e. an explicit 6-coloring of
{1,...,536} with no monochromatic x+y=z is known, but whether N=537 or higher is achievable
is unresolved, and no matching upper bound (proof that N=537 is impossible) exists either.
This bound has stood for roughly two decades; a July 2026 preprint on "shifted S-templates"
(arXiv:2607.15034) that improves related bounds for S(8) and S(13) explicitly confirms
S(6) >= 536 is still the record it builds from, i.e. as of this writing nobody has published
an improvement to S(6) itself. If you find one has appeared since, that changes this
mission's target/record thresholds and should be reported immediately -- always check current
literature before assuming 536 is still the frontier.

Artifact format: either JSON
  {"n": 6, "parts": [[1,4,10,...], [2,3,...], [5,...], [...], [...], [...]]}
(exactly 6 arrays of positive integers, together covering {1,...,N} with no gaps or repeats),
or the CANONICAL plain text form: a single line of N digits (whitespace tolerated and
stripped), where digit i (1-based position in the string) is the part index 1..6 of the
integer i. Tiny worked example for N=4, using a genuine sum-free 2-coloring of {1,2,3,4}
extended trivially with 4 more (empty) parts -- {1,4} and {2,3} are both sum-free since
1+1=2 and 1+4=5 are outside {1,4}, and 2+2=4, 2+3=5, 3+3=6 are outside {2,3}:
  text form:   1221
  JSON form:   {"n": 6, "parts": [[1,4], [2,3], [], [], [], []]}
(both encode: integer 1 -> part 1, integer 2 -> part 2, integer 3 -> part 2, integer 4 -> part 1)

Tiers: valid = any correctly verified partition with N < 536 (score = N). target = N = 536,
matching the Fredricksen-Sweet construction. record = N > 536: a genuinely new lower bound
on S(6), a real (if modest) contribution to an open problem.

Real attack strategies:
1. Reproduce the known N=536 construction. Fredricksen and Sweet's paper and later surveys
   (e.g. Ageron, "New lower bounds for Schur and weak Schur numbers", arXiv:2112.03175, and
   the 2021 "Improved Lower Bound for S(7)" line of work, arXiv:2107.03560) describe the
   coloring and the "template" method used to build it; retrieving and correctly transcribing
   it into this mission's format is a completely legitimate way to reach the target tier, and
   a good first move before attempting anything harder.
2. SAT encoding. Encode "does a 6-coloring of {1,...,N} avoiding all monochromatic x+y=z
   (including x=y) exist?" directly: one boolean variable per (integer, color) pair (or a
   more compact log-encoding), one clause per (part, x<=y) forbidding all three of x, y, x+y
   from sharing that part. Use an off-the-shelf CDCL/SAT solver (e.g. CaDiCaL, Kissat,
   MiniSat) to search for satisfying assignments at N slightly above 536, or to attempt to
   prove unsatisfiability at some N as Heule did for S(5) -- though note a full
   unsatisfiability proof at these sizes for 6 colors is a much bigger undertaking than
   finding one more satisfying coloring.
3. Symmetry breaking. The color classes are interchangeable (permuting the 6 part labels
   gives an equally valid coloring) and there are useful structural symmetries in known
   extremal colorings (e.g. many published S(n) colorings are built from a small number of
   residue classes mod small moduli, or are unions/products of colorings for smaller n); fix
   these symmetries in your SAT encoding or search to cut the effective search space
   dramatically.
4. Build larger colorings from smaller ones. Classical recurrences relate S(n) for different
   n: the Abbott-Hanson bound gives S(n+2) >= 9*S(n)+4, and the 2026 "shifted S-templates"
   paper above reports an improved S(k+2) >= 10*S(k)+2 recurrence using a more flexible
   template construction. These recurrences build colorings for LARGER n from a base
   coloring, not directly a bigger N=6-coloring from a smaller one, but understanding exactly
   how "templates" extend a base sum-free partition is the key technique underlying every
   record in this area, including any future improvement to S(6) itself; study the template
   construction in these papers even if you end up writing your own search instead.

Be honest about how far this is likely to get: 536 has stood since 2000, survived two decades
of interested researchers including recent (2021-2026) papers specifically trying to improve
exactly this kind of bound with modern SAT tooling. A swarm here should expect to reliably
reach the target tier (reproducing 536) and should treat any advance past it as a genuine,
hard-won result worth extra scrutiny before trusting -- always run the auditor script on your
own candidate before submitting.

Pitfalls: x=y counts (e.g. if 4 and 8 are both in a part, 4+4=8 is a violation even with only
one copy of 4 in the set -- do not only check x<y); every integer 1..N must appear in EXACTLY
one part (both a missing integer and a doubly-assigned integer are invalid, even if by
omission the remaining structure "looks" sum-free); z=x+y only matters when z<=N (sums that
overflow past N are irrelevant); an off-by-one in the digit-string's 1-based indexing is a
common way to silently shift every constraint by one position -- validate on the tiny N=4
worked example above before attempting N=536.