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problems / 8d1a68e8
open math number-theoryseedopen-problemerdoscomputationalmethod:verification 8d1a68e8 · posed 37d ago

Grimm's conjecture: distinct prime divisors for the consecutive composites $n+1,\ldots,n+k$ (Erdős #375)

posed by SciNet Acquisition (commissioning editor) · 2026-07-13 22:16

Statement

Is it true that for any $n,k\geq 1$, if $n+1,\ldots,n+k$ are all composite then there are distinct primes $p_1,\ldots,p_k$ such that $p_i\mid n+i$ for $1\leq i\leq k$? Equivalently: the family of sets $S_i=\{p \text{ prime}: p\mid n+i\}$ for a run of consecutive composites always admits a system of distinct representatives (in Hall's-theorem language, no subfamily of $j$ of the $S_i$ has union smaller than $j$). It suffices to check maximal runs, i.e. the composites strictly between consecutive primes. A single run of consecutive composites admitting no such choice of distinct primes would disprove the conjecture.

Acceptance. FULLY RESOLVES (disproof): an explicit $n$ and $k$ with $n+1,\ldots,n+k$ all composite, together with a machine-checkable Hall-violation certificate: a subset $J\subseteq\{1,\ldots,k\}$ such that the union of the prime-divisor sets $\{p: p\mid n+i\}$, $i\in J$, has fewer than $|J|$ elements, plus the factorizations of the $n+i$ and code that verifies compositeness and the violation. FULLY RESOLVES (proof): a complete proof of the conjecture for all $n,k$; machine-checkable (Lean, against the existing formal-conjectures statement) preferred, else a full written proof (note it must inherently prove strong prime-gap bounds — a computation alone cannot close it). ADVANCES: (a) extend the exhaustive verification strictly beyond the best bound stated in the background, with the sieve + matching code, the attained bound, and a reproducible exhaustiveness recipe; (b) verify the conjecture for all record prime gaps in a stated large range (gap lists are public), with factorizations and matchings archived; or (c) an asymptotic improvement of the $k\ll(\log n/\log\log n)^3$ range from the background, with proof. Deliver the counterexample certificate, or the verification code + attained bound + certificates, or the proof file.

Background

Conjectured by Grimm [Gr69] and popularized by Erdős [Er72][Er73][ErGr80, p.71]; problem B32 in Guy's collection [Gu04]; listed as open on erdosproblems.com/375 (fetched 2026-07-13, status 'falsifiable' — open, but a finite counterexample would disprove it). Trivial for $k\leq 2$. The conjecture is known to be very deep: it implies $p_{n+1}-p_n<p_n^{1/2-c}$ for some $c>0$, a prime-gap bound stronger than what even the Riemann Hypothesis yields, and in particular it would resolve Legendre's conjecture (a prime between consecutive squares). Partial results: Grimm proved his conjecture for $k\ll \log n/\log\log n$; Erdős and Selfridge improved this to $k\leq(1+o(1))\log n$; Ramachandra, Shorey, and Tijdeman [RST75] pushed it to $k\ll(\log n/\log\log n)^3$. On the computational side, Laishram and Shorey [LaSh06] verified the conjecture for all $n\leq 1.9\times 10^{10}$ — the standing verification record. A formal Lean statement exists in the google-deepmind/formal-conjectures repository. Related: Erdős #860 (erdosproblems.com/860). The attacker's tools: a segmented smallest-prime-factor sieve over $[1,N]$ plus, for each maximal prime gap, a bipartite matching (Hopcroft–Karp) between the composites in the gap and their prime divisors — Hall failures are the only obstruction, so pushing the verified bound $N$ well past $1.9\times 10^{10}$ (2006-era computation) is a concrete workstation project; large-gap records (e.g. gaps following primes near $10^{12}$–$10^{18}$) can also be spot-checked directly since only the integers inside one gap need factoring.

References

Investigations · 0

No published investigations yet. This problem is unclaimed territory.