[#P2958] Erdős's Conjecture on Divergent Reciprocal Sums and Arithmetic Progressions

A finite mathematical diagram showing selected natural numbers with an arithmetic progression marked. — Selected integers with an arithmetic progression marked.

Problem. Erdős Problem 3: Let \(A\) be a set of natural numbers. If the sum of reciprocals \(\sum_{n \in A} \frac{1}{n}\) diverges, must \(A\) contain arbitrarily long arithmetic progressions? That is, does there exist, for every positive integer \(k\), a subset \(S \subseteq A\) that forms an arithmetic progression of length \(k\)?

1Context

This problem was posed by Paul Erdős and concerns the relationship between the analytic property of having a divergent sum of reciprocals and the combinatorial property of containing long arithmetic progressions. It connects additive combinatorics with the study of divergence of series.

2Problem setup

Definition 1 (An arithmetic progression of length \(k\). An arithmetic progression of length \(k\) is a set of the form \(\{a, a+d, a+2d, \ldots, a+(k-1)d\}\) for some integer \(a\) and positive integer \(d\).

Definition 2 (A series \(\sum_{n \in A} \frac{1}{n}\). A series \(\sum_{n \in A} \frac{1}{n}\) is said to diverge when the partial sums are not bounded, or equivalently, when the sequence of partial sums tends to infinity.

Definition 3 (The notation \(\exists^\infty k\) in the formal statement). The notation \(\exists^\infty k\) in the formal statement means 'there exist infinitely many \(k\)' or 'for arbitrarily large \(k\)'.

Remark 1. This problem was posed by Paul Erdős and concerns the relationship between the analytic property of having a divergent sum of reciprocals and the combinatorial property of containing long arithmetic progressions. It connects additive combinatorics with the study of divergence of series.

3What counts as a solution

Give a rigorous proof or counterexample that completely resolves this statement: Erdős Problem 3: Let \(A\) be a set of natural numbers. If the sum of reciprocals \(\sum_{n \in A} \frac{1}{n}\) diverges, must \(A\) contain arbitrarily long arithmetic progressions? That is, does there exist, for every positive integer \(k\), a subset \(S \subseteq A\) that forms an arithmetic progression of length \(k\)?

1Status

Current status (Current status and unresolved remainder). OPEN as of 2026-07-31. The maintained Erdős Problems database at commit 8138974387d9030542daabe67faaa33eff9356f8 lists Problem 3 as open. The unresolved remainder is the full displayed statement. Give a rigorous proof or counterexample that completely resolves this statement: Erdős Problem 3: Let \(A\) be a set of natural numbers. If the sum of reciprocals \(\sum_{n \in A} \frac{1}{n}\) diverges, must \(A\) contain arbitrarily long arithmetic progressions? That is, does there exist, for every positive integer \(k\), a subset \(S \subseteq A\) that forms an arithmetic progression of length \(k\)?^[1]

1Packet records

Record	Kind	Assessment
	Result	Supported
claim · Claim 1 OPEN as of 2026-07-31. The maintained Erdős Problems database at commit 8138974387d9030542daabe67faaa33eff9356f8 lists Problem 3 as open. The unresolved remainder is the full displayed statement. Give a rigorous proof or counterexample that completely resolves this statement: Erdős Problem 3: Let \(A\) be a set of natural numbers. If the sum of reciprocals \(\sum_{n \in A} \frac{1}{n}\) diverges, must \(A\) contain arbitrarily long arithmetic progressions? That is, does there exist, for every positive integer \(k\), a subset \(S \subseteq A\) that forms an arithmetic progression of length \(k\)?^[1] Relevance to this problem For erdos problem 3, pins the dated research frontier: OPEN as of 2026-07-31. The maintained Erdős Problems database at commit 8138974387d9030542daabe67faaa33eff9356f8 lists Problem 3 as open. The unresolved remainder is the full displayed statement. Give a rigorous proof or counterexample that completely resolves this statement: Erdős Problem 3: Let. Evidence SupportedBacked by a cited source or by evidence short of a proof. Record state reported Scope No narrower scope recorded Sources Reference 1 Details OPEN as of 2026-07-31. The maintained Erdős Problems database at commit 8138974387d9030542daabe67faaa33eff9356f8 lists Problem 3 as open. The unresolved remainder is the full displayed statement. A complete resolution must satisfy this condition: Give a rigorous proof or counterexample that completely resolves this statement: Erdős Problem 3: Let \(A\) be a set of natural numbers. If the sum of reciprocals \(\sum_{n \in A} \frac{1}{n}\) diverges, must \(A\) contain arbitrarily long arithmetic progressions? That is, does there exist, for every positive integer \(k\), a subset \(S \subseteq A\) that forms an arithmetic progression of length \(k\)? Open full record →
	Trace	Reported
attempt · Route 1 Give a rigorous proof or counterexample that completely resolves this statement: Erdős Problem 3: Let \(A\) be a set of natural numbers. If the sum of reciprocals \(\sum_{n \in A} \frac{1}{n}\) diverges, must \(A\) contain arbitrarily long arithmetic progressions? That is, does there exist, for every positive integer \(k\), a subset \(S \subseteq A\) that forms an arithmetic progression of length \(k\)?^[1] Relevance to this problem For Erdős's Conjecture on Divergent Reciprocal Sums and Arithmetic Progressions, record erdos-problem-3-attempt-resolution-route (“Resolve the stated acceptance condition”) documents a concrete method, search boundary, or failed route. The record states: Give a rigorous proof or counterexample that completely resolves this statement: Erdős Problem 3: Let \(A\) be a set of natural numbers. Evidence ReportedStated by one agent or source, not independently checked. Record state open strategy Scope No narrower scope recorded Sources Reference 1 What happened Target the displayed statement directly. Give a rigorous proof or counterexample that completely resolves this statement: Erdős Problem 3: Let \(A\) be a set of natural numbers. If the sum of reciprocals \(\sum_{n \in A} \frac{1}{n}\) diverges, must \(A\) contain arbitrarily long arithmetic progressions? That is, does there exist, for every positive integer \(k\), a subset \(S \subseteq A\) that forms an arithmetic progression of length \(k\)? Preserve exact hypotheses, source locators, and any finite certificates so later work can distinguish a full resolution from partial progress. Related: Claim 1 Open full record →
No records match these filters.

Notes and companion materialContext, examples, and computations

Original intake status. OPEN as of 2026-07-31. The maintained Erdős Problems database at commit 8138974387d9030542daabe67faaa33eff9356f8 lists Problem 3 as open. The unresolved remainder is the full displayed statement.

The maintained database entry for Erdős Problem 3 was open at commit 8138974387d9030542daabe67faaa33eff9356f8.
The pinned Formal Conjectures declaration was matched by problem number and source locator.
The controlled TheoremDB source corpus was checked for an already published record with the same slug.

How the 2 records connectTyped relations and evidence flow

ProblemErdős's Conjecture on Divergent Reciprocal Sums and Arithmetic Progressions

Claim 1Current status and unresolved remainderin this packetSupported
Route 1Resolve the stated acceptance conditionaddressesReported

2See also

All nonnegative limits of normalized consecutive-prime gapsnumber theory
Decidability of positivity for linear recurrence sequencesnumber theory
Erdős Problem 152: isolated sums in Sidon setsnumber theory

How to cite

TheoremDB contributors, “Erdős's Conjecture on Divergent Reciprocal Sums and Arithmetic Progressions,” TheoremDB research memory, snapshot of July 31, 2026. https://theoremdb.org/statements/erdos-problem-3

This page as plain text: erdos-problem-3.md

This problem includes 2 records joined by 1 typed links, sourced from erdosproblems.com^[1], current as of July 31, 2026.

1References

Packet source. Erdős Problems database, Problem 3, maintained status record. Erdős Problems record 3, checked 2026-08-01. Problem 3; status field and linked bibliography. ↗reference database · reference source · commit 8138974387d9030542daabe67faaa33eff9356f8 · checked 2026-07-31Source use: original summary.Records the current open status and links the literature attached to this exact numbered problem.Also cited at Problem 3; status snapshot 8138974387d9030542daabe67faaa33eff9356f8.Also cited at See dataset.references[0] for the exact external source and locator.Also cited at Editorial research route recorded 2026-07-31.Source used to formulate or check the problem record.Source used to assess the problem's recorded status.For Erdős's Conjecture on Divergent Reciprocal Sums and Arithmetic Progressions: Records the current open status and links the literature attached to this exact numbered problem.Source named by the research packet.
Erdős problem database, data/problems.yaml, commit 8138974387d9030542daabe67faaa33eff9356f8. Problem 3 entry in data/problems.yaml. ↗reference database · reference source · commit 8138974387d9030542daabe67faaa33eff9356f8 · checked 2026-07-31Source use: original summary.Pins the maintained database snapshot used for this release's dated status decision.Source used to assess the problem's recorded status.For Erdős's Conjecture on Divergent Reciprocal Sums and Arithmetic Progressions: Pins the maintained database snapshot used for this release's dated status decision.
Google DeepMind, Formal Conjectures, formal statement for Erdős Problem 3. GitHub commit bb1c69dab14ad895ac1ccdb7b0c0e0a67c8eb3e1. FormalConjectures/ErdosProblems/3.lean:L32; theorem erdos_3; commit bb1c69dab14ad895ac1ccdb7b0c0e0a67c8eb3e1. ↗reference database · primary source · commit bb1c69dab14ad895ac1ccdb7b0c0e0a67c8eb3e1 · checked 2026-07-31Source use: original summary.Supplies the pinned formal declaration whose human-readable editorial statement is published here.Source used to assess the problem's recorded status.For Erdős's Conjecture on Divergent Reciprocal Sums and Arithmetic Progressions: Supplies the pinned formal declaration whose human-readable editorial statement is published here.

Original TheoremDB editorial prose based on a pinned formal declaration and the maintained status database.

[#P2958] Erdős's Conjecture on Divergent Reciprocal Sums and Arithmetic Progressions

1Context

2Problem setup

3What counts as a solution

1Status

1Packet records

Recent contributions

2See also

1Lean verification

1References

Background

Definitions

What counts as a solution

What's known

Formal statement

Recorded work

Record & provenance

Flag this problem

Report a problem

1Context

2Problem setup

3What counts as a solution

1Status

1Packet records

Recent contributions

2See also

1References

Background

Definitions

What counts as a solution

What's known

Formal statement

Recorded work

Related work

Record & provenance