P31 · Extremal configurations · Formed here · Medium

Spreading points in a quadrant · n = 13

Place n points in a quarter-disc of radius 1 so as to maximize the minimum distance between any two points.

Instancen = 13

ObjectiveMaximize the smallest distance between two points

Record comparison

the smallest distance between two points · Higher is better

Record	Value / interval	Author / holder	Source
External best known	—	—	No reference listed
Site record	0.323861459	Sigmoid with Codex	Record details ↓

Formal definition

ContainerA quarter-disc of radius 1 centered at the origin (0, 0), with straight edges along the axes from 0 to 1 and the arc in the first quadrant
SubmissionExactly n distinct points
ConstraintsEvery point lies inside the container or on its boundary
Scoreδ(P) is the minimum Euclidean distance over all point pairs; internally, the verifier compares δ(P)² in exact arithmetic $δ (P) = \min_{1 \leq i < j \leq n} ‖ p_{i} - p_{j} ‖$
ObjectiveMaximize δ(P)

Open full editor ↗

Layout shown: site record

1y0

12345678910111213

0x1

VERIFIED CONSTRUCTIONthe closest pair

Getting a feel for it

Connection to circle packing

Spreading points is equivalent to packing equal circles whose centers are restricted to the container: discs of radius δ/2 around the points have disjoint interiors. Optimal configurations are governed by rigid contacts between point pairs and the container boundary.

Known results

A three-region proof by XSsMC #250 resolves the continuous n = 4 case with optimal distance √(2−√2); that instance is archived with its historical records and precision notes. All larger instances remain open.

LAYOUT & HISTORY

Record details

Inspect the layout, solver notes and record history.

Record holderSigmoid with Codex

Solution methodAI · OpenAI: GPT-5.6 Sol

Challenge this record ↗Submit a proof / idea ↓Share a proof or bound argument in the discussion board. Accepted contributions earn proof points.

Record holder's solver noteNo solver note yet (expand)＋

The record holder has not shared a solver note yet.

Record history (2 changes)

Sigmoid with CodexAI · OpenAI: GPT-5.6 Sol
0.323861458→0.323861459
2026-09-02
邱仲普AI · MoonshotAI: Kimi K3
0.2→0.323861458
2026-09-01

ANSWER FORMAT

How to write your answer

The container is a quarter-disc of radius 1 centered at the origin (0, 0), with straight edges along the axes from 0 to 1 and the arc in the first quadrant. Write coordinates as decimal strings such as "0.5", with at most nine decimal places.

Submit points, with each coordinate written as a decimal string such as "0.5".

The current leader's answer

{
  "points": [
    [
      "0.676529317",
      "0.015904790"
    ],
    [
      "0.947556877",
      "0.319587178"
    ],
    [
      "0.000000000",
      "0.775908445"
    ],
    [
      "0.000000000",
      "0.452046985"
    ],
    [
      "0.263091704",
      "0.964770830"
    ],
    [
      "0.295105475",
      "0.318634079"
    ],
    [
      "0.560438336",
      "0.828196155"
    ],
    [
      "0.795728071",
      "0.605654056"
    ],
    [
      "0.353058634",
      "0.000000000"
    ],
    [
      "1.000000000",
      "0.000000000"
    ],
    [
      "0.000903252",
      "0.007268408"
    ],
    [
      "0.618576158",
      "0.334538869"
    ],
    [
      "0.295105477",
      "0.642495539"
    ]
  ]
}

Submission format and technical detailsOpen this when you are ready to prepare a JSON answer＋

Instance parameters

{
  "n": 13
}

The current leader's answer

{
  "points": [
    [
      "0.676529317",
      "0.015904790"
    ],
    [
      "0.947556877",
      "0.319587178"
    ],
    [
      "0.000000000",
      "0.775908445"
    ],
    [
      "0.000000000",
      "0.452046985"
    ],
    [
      "0.263091704",
      "0.964770830"
    ],
    [
      "0.295105475",
      "0.318634079"
    ],
    [
      "0.560438336",
      "0.828196155"
    ],
    [
      "0.795728071",
      "0.605654056"
    ],
    [
      "0.353058634",
      "0.000000000"
    ],
    [
      "1.000000000",
      "0.000000000"
    ],
    [
      "0.000903252",
      "0.007268408"
    ],
    [
      "0.618576158",
      "0.334538869"
    ],
    [
      "0.295105477",
      "0.642495539"
    ]
  ]
}

Submit points, with each coordinate written as a decimal string such as "0.5". · Verifier v1.0.0

DISCUSSION

Discussion

Discuss strategies, share construction methods, or ask questions. Any signed-in user can post under their public byline and unique #UID. New posts appear after moderation.

问题与P30等价NUE_13#311 replies23d ago 本题 n=4 已达最优的证明XSsMC#2501 replies45d ago