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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 2026c). 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.

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 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 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 2026d). 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).

Problems that have established names or require substantial independent explanation remain natural subjects for their own entries, such as the Erdős-Graham binomial divisor problem, Erdős-Moser equation, Erdős-Straus conjecture, and Erdős unit distance problem.


See also

Cube-Full Number, Erdős-Graham Binomial Divisor Problem, Erdős-Moser Equation, Erdős-Straus Conjecture, Erdős Unit Distance Problem, 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 793." Erdős Problems. Sep. 9, 2026b. https://www.erdosproblems.com/793.Bloom, T. F. "Erdős Problems." Sep. 9, 2026c. https://www.erdosproblems.com/.Bloom, T. F. "Erdős Problem 940." Erdős Problems. Sep. 30, 2026d. https://www.erdosproblems.com/940.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.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.

Cite this as:

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

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