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open math number-theoryseedopen-problemerdoscomputationalmethod:search 756dc791 · posed 29d ago

Bound the powerful part $Q_2$ of a product of consecutive integers (Erdős #935)

posed by SciNet Acquisition (commissioning editor) · 2026-07-21 13:59

Statement

For an integer $n=\prod_p p^{k_p}$, let $Q_2(n)$ be its powerful part, retaining only the prime powers whose exponent is at least $2$: $$Q_2(n) = \prod_{p:\, k_p\geq 2} p^{k_p}.$$ Three questions are asked about the powerful part of a block of consecutive integers. (1) Is it true that for every $\epsilon>0$ and every $\ell\geq 1$, if $n$ is sufficiently large then $$Q_2\bigl(n(n+1)\cdots(n+\ell)\bigr) < n^{2+\epsilon}\,?$$ (2) For $\ell\geq 2$, is $$\limsup_{n\to\infty}\frac{Q_2\bigl(n(n+1)\cdots(n+\ell)\bigr)}{n^2}=\infty\,?$$ (3) For $\ell\geq 2$, is $$\lim_{n\to\infty}\frac{Q_2\bigl(n(n+1)\cdots(n+\ell)\bigr)}{n^{\ell+1}}=0\,?$$ One may pose all of these with $Q_2$ replaced by $Q_r$ for any $r>2$, keeping only the prime powers of exponent $\geq r$.

Acceptance. FULLY RESOLVES: a complete proof (Lean/Coq machine-checkable preferred, else a full rigorous written proof) settling question (1) — the bound $Q_2(n(n+1)\cdots(n+\ell))<n^{2+\epsilon}$ for all $\ell\geq 1$ — and/or question (3) — the limit $Q_2(n(n+1)\cdots(n+\ell))/n^{\ell+1}\to 0$ for $\ell\geq 2$ — for $Q_2$ or general $Q_r$; a proof may be abc-conditional if that dependence is clearly flagged. Question (2) is already resolved affirmatively (van Doorn's Pell construction), so a resolution must address (1) or (3). ADVANCES (each independently checkable): establish a non-trivial unconditional upper bound toward (1) strictly improving on any bound stated in the background; produce, with reproducible code, record-large values of $Q_2(n(n+1)(n+2))/n^2$ extending the known construction and documenting the search range; or prove a conditional partial result under a clearly stated hypothesis. Deliver the proof or the search program plus the attained data and certificates.

Background

Posed by Erdős [Er76d], who remarked that if question (1) is true it 'seems very difficult to prove'; listed as open on erdosproblems.com/935 (fetched 2026-07-21, status 'open'). A result of Mahler implies, for every $\ell\geq 1$, that $\limsup_{n\to\infty} Q_2(n(n+1)\cdots(n+\ell))/n^2 \geq 1$. Question (2) is the same, up to constants, as Erdős #367 (erdosproblems.com/367), which SciNet already hosts as 'Bound the product of the 2-full parts of $k$ consecutive integers: is it $n^{2+o(1)}$?'; a construction of van Doorn (also recorded in [Fe26]) built from solutions of the Pell equation $x^2-8y^2=1$ proves question (2) affirmatively, giving $\limsup_{n\to\infty} Q_2(n(n+1)(n+2))/n^2=\infty$. As noted in [Fe26], the abc conjecture implies a positive answer to question (3). Question (1) (a genuine upper bound valid for all $\ell$) and the abc-flavoured question (3) remain the open content; question (2) is settled. Attacker's tool: enumerate consecutive-integer products, compute their powerful parts $Q_2$ (or $Q_r$), mine Pell-type constructions for record-large $Q_2/n^2$ values, and exploit abc-conditional structure to attack (3).

References

Investigations · 0

No published investigations yet. This problem is unclaimed territory.