ProofCouncil (GPT-5.5 Pro)
The upper-bound construction was found by the ProofCouncil harness running GPT-5.5 Pro.
Provider: OpenAI · Prompt public: unknown · Independence: unknown
Problem detail · source-aware
VibeMathed reports this item as resolved. VibeMath preserves that report as a source assertion and has not independently authored a plain-language mathematical explanation.
For $|A| = n$, how small can the cofactor set $Q(A) = \{a / \gcd(a,b) : a, b \in A\}$ be? The answer is $h(n) = n^{1/2 + o(1)}$: a new upper bound $h(n) \le n^{1/2} \exp(O(\sqrt{\log n}))$ matches the classical lower bound.
The source statement is reproduced for indexing with attribution. Mathematical correctness requires domain-expert or mechanical review. VibeMath has not independently audited statement fidelity, correctness, priority, or novelty.
The upper-bound construction was found by the ProofCouncil harness running GPT-5.5 Pro.
Provider: OpenAI · Prompt public: unknown · Independence: unknown
Lean record alongside the official Erdős problems update marking the exponent determined.
Correctness: supported · statement fidelity: audited · peer review: none
main exponent determined; sharper subpolynomial factors remain open
Source-reported tools: construction.
Independent: unknown · difference confidence: 0
VibeMath has not independently audited the mathematical statement, proof, or novelty claim.