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Erdős Problems


The Erdős problems are a large collection of questions posed or promoted by Paul Erdős and his collaborators (Bloom 2026d). They range across number theory, combinatorics, graph theory, geometry, and related areas. Bloom's online Erdős Problems database listed 1217 numbered problems as of Sep. 9, 2026, together with their sources, status, references, and discussion. The numbers are database identifiers rather than established names for the individual questions.

The following table links selected problem numbers to their corresponding named problems or related mathematical topics (Bloom 2026d).

Recent results on individual problems include the following.

Problem 302 asks how large a subset A subset= {1,...,n} can be if no distinct a,b,c in A satisfy 1/a=1/b+1/c. Writing f(n) for the maximum cardinality, the problem asks in particular whether f(n)=(1/2+o(1))n, with o(1) as in little-O notation (Erdős and Graham 1980, Bloom 2026a). A Lean development directed by Sodelin (2026), with the argument, code, and formalization produced by ChatGPT/Codex, reported f(732)=f(731), f(733)=f(732)+1, and f(734)=f(732)+2. The first relation follows from an isolated component in the hypergraph of forbidden triples containing the five vertices 122, 183, 244, 366, and 732. Every admissible selection from this component contains at most three of them and can be replaced by 122, 183, and 244. Exact certificates show that neither 733 nor 734 belongs to a forbidden triple on {1,...,734}. The values of f(n) for n=1, 2, ... begin 1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 10, 10, 11, ... (OEIS A390395). This tabulation reaches f(731)=606, so the relations above give f(732)=606, f(733)=607, and f(734)=608. The development proves the three relations but not the external value f(731)=606. As of Sep. 25, 2026, independent human review had not established either that the formal statement matches the classical problem or that the finite result is new. The asymptotic Problem 302 remained open (VibeMathed 2026c).

Problem 374 asks for the orders of growth of the counting functions for factorial square products requiring at least three and at most six factors (Bloom 2026f). Yudin (2026) determined these orders of growth and confirmed the conjectured linear growth for integers requiring six factors. The existence of limiting densities for integers requiring four, five, or six factors remains open.

Problem 793 asks for the maximum cardinality F(n) of a subset A of {1,...,n} such that abc whenever a, b, and c are distinct members of A. The recorded question is whether F(n)=pi(n)+(C+o(1))n^(2/3)(lnn)^(-2) for some constant C. Bloom (2026b) reports that GPT-5.6 Sol, prompted by Przemek Chojecki, gave a Lean-verified argument with

 F(n)=pi(n)+((27)/2+o(1))(n^(2/3))/((lnn)^2).

Here pi(n) is the prime counting function, and o(1) denotes a quantity tending to 0 as n->infty in little-O notation. This determines the proposed constant as C=27/2 (Bloom 2026b, VibeMathed 2026b). No independent specialist review had been reported as of Sep. 9, 2026.

Problem 809, the Burr-Erdős-Graham-Sós conjecture, was resolved by Bucić et al. (2026) for odd cycle graphs of length at least 9 and by Shahab (2026) for the remaining case of the cycle graph C_7 (Bloom 2026c).

Problem 940 asks, for every integer r>=3, whether infinitely many positive integers are not sums of at most r r-full, or r-powerful, numbers, meaning numbers m such that p|m implies p^r|m for every prime number p. It also asks whether the integers representable by at most r such summands have natural density zero (Bloom 2026e). For r=3, the summands are cube-full numbers. Beyer de Ryke (2026) proved the stronger conclusion that the positive integers not representable by at most three cube-full numbers have positive lower natural density. This resolves the first question for r=3, while the density-zero question for r=3 remains open.

For an integer k>=1, let n_k be the least integer n>2k such that the product (n-k)(n-k+1)...(n-1) has no prime factor in the interval (k,2k). Erdős (1979) conjectured that n_k grows faster than every fixed power of k. Van Doorn and Tang (2026) reported the stronger bound

 n_k>exp((ln^2k)/(20lnlnk))

for all sufficiently large k. The paper credits ChatGPT 5.5 Pro with the core idea of adapting Konyagin's argument and supplies supporting Lean formalizations produced by Aristotle. Independent specialist review and an external audit of the formalization had not been reported as of Sep. 21, 2026 (VibeMathed 2026a).


See also

Burr-Erdős-Graham-Sós Conjecture, Cube-Full Number, Erdős-Graham Binomial Divisor Problem, Erdős-Moser Equation, Erdős-Straus Conjecture, Erdős Unit Distance Problem, Factorial Square Products, Unsolved Problems

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References

Beyer de Ryke, B. "A Density Deficit for Sums of Three Cube-Full Numbers." 26 Jul 2026. https://arxiv.org/abs/2609.35772.Bloom, T. F. "Erdős Problem 302." Erdős Problems. Sep. 25, 2026a. https://www.erdosproblems.com/302.Bloom, T. F. "Erdős Problem 374." Erdős Problems. Oct. 2, 2026f. https://www.erdosproblems.com/374.Bloom, T. F. "Erdős Problem 793." Erdős Problems. Sep. 9, 2026b. https://www.erdosproblems.com/793.Bloom, T. F. "Erdős Problem 809." Erdős Problems. Oct. 1, 2026c. https://www.erdosproblems.com/809.Bloom, T. F. "Erdős Problems." Sep. 9, 2026d. https://www.erdosproblems.com/.Bloom, T. F. "Erdős Problem 940." Erdős Problems. Sep. 30, 2026e. https://www.erdosproblems.com/940.Bucić, M.; Chen, K.; and Ma, J. "On a Maximal Anti-Ramsey Conjecture of Burr, Erdős, Graham, and Sós." 24 Mar 2026. https://arxiv.org/abs/2603.18952.Erdős, P. "Some Unconventional Problems in Number Theory." Acta Math. Acad. Sci. Hungar. 33, 71-80, 1979.Erdős, P. and Graham, R. L. Old and New Problems and Results in Combinatorial Number Theory. Geneva, Switzerland: L'Enseignement Mathématique Université de Genève, Vol. 28, 1980.Shahab, A. "The Burr-Erdős-Graham-Sós Conjecture for the Seven-Cycle." 29 Sep 2026. https://arxiv.org/abs/2609.38286.Sodelin. "Old Conjecture Probes: Finite Results for Erdős Problem 302." 2026. https://github.com/Sodelin/oldest-conjecture-/tree/ced445d951ea043fda41b03044192838a838b0f3.Sloane, N. J. A. Sequence A390395 in "The On-Line Encyclopedia of Integer Sequences."van Doorn, W. and Tang, Q. "Consecutive Integers Free of Certain Prime Factors." 18 Jun 2026. https://arxiv.org/abs/2606.19863.VibeMathed. "Erdős's Conjecture on Consecutive Integers Free of Certain Prime Factors." 18 Jun 2026a. https://vibemathed.com/problem/erdos-consecutive-integers-prime-factors.VibeMathed. "Erdős Problem 793." Sep. 9, 2026b. https://vibemathed.com/problem/erdos-793.VibeMathed. "Reciprocal-Triple-Free Sets: Finite Maxima through 734." Sep. 7, 2026c. https://vibemathed.com/problem/reciprocal-triple-free-sets-the-finite-plateau-at-732.Yudin, F. "Square Products of Factorials and a Conjecture of Erdős and Graham." 1 Oct 2026. https://arxiv.org/abs/2610.01899.

Cite this as:

Weisstein, Eric W. "Erdős Problems." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/ErdosProblems.html

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