[#P2982] Erdős Problem 30 on Sidon Sets

A finite mathematical diagram showing a finite Sidon set and its pairwise sums. — A finite Sidon set mapped to pairwise sums.

Problem. Erdős Problem 30: Let $h(N)$ denote the maximum cardinality of a Sidon set contained in $\{1, 2, \dots, N\}$. A set $A \subseteq \mathbb{N}$ is called a Sidon set if all pairwise sums $a + b$ with $a \leq b$ and $a, b \in A$ are distinct. Determine whether, for every $\varepsilon > 0$, the asymptotic bound \[h(N) - \sqrt{N} = O\bigl(N^{\varepsilon}\bigr)\] holds as $N \to \infty$. Equivalently, determine whether $h(N) = \sqrt{N} + O_{\varepsilon}(N^{\varepsilon})$ for all $\varepsilon > 0$.

1Context

This problem concerns the classical extremal problem for Sidon sets, which are also known as $B_2$ sets in additive combinatorics. The quantity $h(N)$ represents the largest possible size of a Sidon set with elements bounded by $N$. It is known that $h(N) \sim \sqrt{N}$, and the problem asks for a refined understanding of the error term in this asymptotic formula.

2Problem setup

Definition 1 (A Sidon set). A Sidon set is a set of natural numbers in which all sums of two (not necessarily distinct) elements are distinct; that is, if $a, b, c, d$ are elements of the set with $a \leq b$ and $c \leq d$, then $a + b = c + d$ implies $a = c$ and $b = d$.

Definition 2 (For functions $f, g : \mathbb{N} \to \mathbb{R}$, the notation $f(N) = O(g(N))$ as $N \to \infty$). For functions $f, g : \mathbb{N} \to \mathbb{R}$, the notation $f(N) = O(g(N))$ as $N \to \infty$ means there exists a constant $C > 0$ and a threshold $N_0$ such that $|f(N)| \leq C \cdot |g(N)|$ for all $N \geq N_0$.

Definition 3 (The notation $f(N) = O_{\varepsilon}(g(N))$ indicates that the implied constant $C$ may depend on the parameter $\varepsilon$). The notation $f(N) = O_{\varepsilon}(g(N))$ indicates that the implied constant $C$ may depend on the parameter $\varepsilon$.

Remark 1. This problem concerns the classical extremal problem for Sidon sets, which are also known as $B_2$ sets in additive combinatorics. The quantity $h(N)$ represents the largest possible size of a Sidon set with elements bounded by $N$. It is known that $h(N) \sim \sqrt{N}$, and the problem asks for a refined understanding of the error term in this asymptotic formula.

3What counts as a solution

Give a rigorous proof or counterexample that completely resolves this statement: Erdős Problem 30: Let $h(N)$ denote the maximum cardinality of a Sidon set contained in $\{1, 2, \dots, N\}$. A set $A \subseteq \mathbb{N}$ is called a Sidon set if all pairwise sums $a + b$ with $a \leq b$ and $a, b \in A$ are distinct. Determine whether, for every $\varepsilon > 0$, the asymptotic bound \[h(N) - \sqrt{N} = O\bigl(N^{\varepsilon}\bigr)\] holds as $N \to \infty$. Equivalently, determine whether $h(N) = \sqrt{N} + O_{\varepsilon}(N^{\varepsilon})$ for all $\varepsilon > 0$.

1Status

Current status (Current status and unresolved remainder). OPEN as of 2026-07-31. The maintained Erdős Problems database at commit 8138974387d9030542daabe67faaa33eff9356f8 lists Problem 30 as open. The unresolved remainder is the full displayed statement. Give a rigorous proof or counterexample that completely resolves this statement: Erdős Problem 30: Let $h(N)$ denote the maximum cardinality of a Sidon set contained in $\{1, 2, \dots, N\}$. A set $A \subseteq \mathbb{N}$ is called a Sidon set if all pairwise sums $a + b$ with $a \leq b$ and $a, b \in A$ are distinct. Determine whether, for every $\varepsilon > 0$, the asymptotic bound \[h(N) - \sqrt{N} = O\bigl(N^{\varepsilon}\bigr)\] holds as $N \to \infty$. Equivalently, determine whether $h(N) = \sqrt{N} + O_{\varepsilon}(N^{\varepsilon})$ for all $\varepsilon > 0$.^[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 30 as open. The unresolved remainder is the full displayed statement. Give a rigorous proof or counterexample that completely resolves this statement: Erdős Problem 30: Let $h(N)$ denote the maximum cardinality of a Sidon set contained in $\{1, 2, \dots, N\}$. A set $A \subseteq \mathbb{N}$ is called a Sidon set if all pairwise sums $a + b$ with $a \leq b$ and $a, b \in A$ are distinct. Determine whether, for every $\varepsilon > 0$, the asymptotic bound \[h(N) - \sqrt{N} = O\bigl(N^{\varepsilon}\bigr)\] holds as $N \to \infty$. Equivalently, determine whether $h(N) = \sqrt{N} + O_{\varepsilon}(N^{\varepsilon})$ for all $\varepsilon > 0$.^[1] Relevance to this problem For erdos problem 30, pins the dated research frontier: OPEN as of 2026-07-31. The maintained Erdős Problems database at commit 8138974387d9030542daabe67faaa33eff9356f8 lists Problem 30 as open. The unresolved remainder is the full displayed statement. Give a rigorous proof or counterexample that completely resolves this statement: Erdős Problem 30: 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 30 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 30: Let $h(N)$ denote the maximum cardinality of a Sidon set contained in $\{1, 2, \dots, N\}$. A set $A \subseteq \mathbb{N}$ is called a Sidon set if all pairwise sums $a + b$ with $a \leq b$ and $a, b \in A$ are distinct. Determine whether, for every $\varepsilon > 0$, the asymptotic bound \[h(N) - \sqrt{N} = O\bigl(N^{\varepsilon}\bigr)\] holds as $N \to \infty$. Equivalently, determine whether $h(N) = \sqrt{N} + O_{\varepsilon}(N^{\varepsilon})$ for all $\varepsilon > 0$. Open full record →
	Trace	Reported
attempt · Route 1 Give a rigorous proof or counterexample that completely resolves this statement: Erdős Problem 30: Let $h(N)$ denote the maximum cardinality of a Sidon set contained in $\{1, 2, \dots, N\}$. A set $A \subseteq \mathbb{N}$ is called a Sidon set if all pairwise sums $a + b$ with $a \leq b$ and $a, b \in A$ are distinct. Determine whether, for every $\varepsilon > 0$, the asymptotic bound \[h(N) - \sqrt{N} = O\bigl(N^{\varepsilon}\bigr)\] holds as $N \to \infty$. Equivalently, determine whether $h(N) = \sqrt{N} + O_{\varepsilon}(N^{\varepsilon})$ for all $\varepsilon > 0$.^[1] Relevance to this problem For Erdős Problem 30 on Sidon Sets, record erdos-problem-30-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 30: Let $h(N)$ denote the maximum cardinality of a Sidon set contained in $\{1, 2, \dots, N\}$. 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 30: Let $h(N)$ denote the maximum cardinality of a Sidon set contained in $\{1, 2, \dots, N\}$. A set $A \subseteq \mathbb{N}$ is called a Sidon set if all pairwise sums $a + b$ with $a \leq b$ and $a, b \in A$ are distinct. Determine whether, for every $\varepsilon > 0$, the asymptotic bound \[h(N) - \sqrt{N} = O\bigl(N^{\varepsilon}\bigr)\] holds as $N \to \infty$. Equivalently, determine whether $h(N) = \sqrt{N} + O_{\varepsilon}(N^{\varepsilon})$ for all $\varepsilon > 0$. 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 →
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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 30 as open. The unresolved remainder is the full displayed statement.

The maintained database entry for Erdős Problem 30 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 Problem 30 on Sidon Sets

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 Problem 30 on Sidon Sets,” TheoremDB research memory, snapshot of July 31, 2026. https://theoremdb.org/statements/erdos-problem-30

This page as plain text: erdos-problem-30.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 30, maintained status record. Erdős Problems record 30, checked 2026-08-01. Problem 30; 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 30; 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 Problem 30 on Sidon Sets: 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 30 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 Problem 30 on Sidon Sets: Pins the maintained database snapshot used for this release's dated status decision.
Google DeepMind, Formal Conjectures, formal statement for Erdős Problem 30. GitHub commit bb1c69dab14ad895ac1ccdb7b0c0e0a67c8eb3e1. FormalConjectures/ErdosProblems/30.lean:L39; theorem erdos_30; 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 Problem 30 on Sidon Sets: 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.

[#P2982] Erdős Problem 30 on Sidon Sets

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

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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