Wiki
Wiki

Research notes on every problem, and a library of the papers behind them. Built from the open erdos repository.

Updated


Claim. The answer to Problem 379 is yes: lim sup⁡n→∞S(n)=∞\limsup_{n\to\infty}S(n)=\infty, where S(n)S(n) is the largest ss such that every (nk)\binom{n}{k} with 1≤k<n1\le k<n is divisible by psp^s for some prime pp depending on kk. The proof emerged in the problem's discussion thread on the site between 27 and 28 August 2025, from an exchange among Stijn Cambie, Vjekoslav Kovač and Terence Tao, with Tao's comment of 28 August 2025 giving the complete argument. It is a construction: let r≥2r\ge2 and let pp be a prime with p>2r−1p>2^{r-1}; then n=2φ(pr)n=2^{\varphi(p^r)} has S(n)≥rS(n)\ge r. For such nn every (nk)\binom{n}{k} with 1≤k<n1\le k<n is divisible by 2r2^r or by prp^r. The prime 22 is handled through the identity (nk)k=(n−1k−1)n\binom{n}{k}k=\binom{n-1}{k-1}n: since n=2φ(pr)n=2^{\varphi(p^r)}, either 2r∣(nk)2^r\mid\binom{n}{k} or 2φ(pr)−r+1∣k2^{\varphi(p^r)-r+1}\mid k. The prime pp is handled through Euler's theorem, pr∣n−1p^r\mid n-1, and the identity (nk)k(k−1)=(n−2k−2)(n−1)n\binom{n}{k}k(k-1)=\binom{n-2}{k-2}(n-1)n, which transfers the factor prp^r of n−1n-1 to (nk)\binom{n}{k} when pp divides neither kk nor n−kn-k, hence not k−1k-1; the remaining cases are excluded by the size condition p>2r−1p>2^{r-1}. Taking r→∞r\to\infty with a prime p>2r−1p>2^{r-1} for each rr gives the unbounded sequence. The site also records a simpler construction, n=32kn=3^{2^k}, from an Art of Problem Solving discussion; it is not credited to a named author and has no page here.

Formalization. Tao's Lean development, linked above at a pinned commit of Tao's analysis repository, states in its header that it formalizes a proof of the problem arising from the conversations among the three and points to the thread; its final theorem is the limsup statement with SS defined as the supremum above. The file was first committed on 28 August 2025. The formal-conjectures statement file for the problem names two formal proofs: Tao's file and a proof of erdos_379 at a commit of a contributor's fork that GitHub no longer serves. That proof was the first commit of a pull request to formal-conjectures, whose second commit removed the proof body and kept only the link before the merge of 13 April 2026, so the merged statement stays unproved; the proof is linked above at that first commit; its description says that it follows the argument of Cambie, Kovač and Tao, its helper lemmas are headed as coming from Tao's proof, and its author records assistance from Claude (Anthropic) for the Lean translation. This corpus has not built or audited either development, so neither is listed as evidence.

Depends on. No page of this wiki.

Acceptance. Thomas Bloom, the site's curator, marks the problem proved, credits Cambie, Kovač and Tao on the problem page (last edited 12 January 2026) and records the Lean formalization in the site's label; the community database lists the problem's status as proved (Lean) as of its last update, dated 31 August 2025. There is no refereed write-up and the result exists only as the thread posts and the Lean file; the acceptance rests on the curator's documented review.