All open problems
Source labels openChecked July 26, 2026

WikipediaGeometry

Packing

What is the smallest circle that can contain 15 unit circles?

Mathematical statement

What is the smallest circle that can contain 15 unit circles?

Reference: Graham RL, Lubachevsky BD, Nurmela KJ, Ostergard PRJ. Dense packings of congruent circles in a circle. Discrete Math 1998;181:139–154.

Statement source: Wikipedia statement material

Statement terms: CC-BY-SA-4.0

Attributed source material. Reuse must follow the linked attribution and share-alike terms.

Statement artifacts, not proofs

These records expose exact Lean propositions and statement-only wrappers. Defining a proposition does not supply a proof of it. A placeholder-bearing target also contains no proof. Elaboration checks syntax and types; it does not certify that a formalization perfectly captures every nuance of the informal problem.

Pinned Lean formulation 1

least_fifteen_circle_packing_in_circle

Canonical source
Complete statement target, proof intentionally absentLean 4
theorem least_fifteen_circle_packing_in_circle :    IsLeast {r :  | Nonempty (Packing 15 UnitCircle (Circle r))} answer(sorry) := by  sorry
Statement source
Formal Conjectures
Lean version
v4.27.0
Placeholder
Present; no proof artifact
Source evidence
Pinned source index
Fidelity review
Community formulation

References