Circle packing in a circle

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Circle packing in a circle is a two-dimensional packing problem with the objective of packing unit circles into the smallest possible larger circle.

Contents

Table of solutions, 1 ≤ n ≤ 20

If more than one equivalent solution exists, all are shown. [1]

Number of
unit circles
Enclosing circle radiusDensityOptimalityDiagram
111.0000Trivially optimal. Disk pack1.svg
220.5000Trivially optimal. Disk pack2.svg
3 ≈ 2.155...0.6466...Trivially optimal. Disk pack3.svg
4 ≈ 2.414...0.6864...Trivially optimal. Disk pack4.svg
5 ≈ 2.701...0.6854...Proved optimal by Graham
(1968) [2]
Disk pack5.svg
630.6666...Proved optimal by Graham
(1968) [2]
Disk pack6.svg Disk pack6 2.svg
730.7777...Trivially optimal. Disk pack7.svg
8 ≈ 3.304...0.7328...Proved optimal by Pirl
(1969) [3]
Disk pack8.svg
9 ≈ 3.613...0.6895...Proved optimal by Pirl
(1969) [3]
Disk pack9.svg
103.813...0.6878...Proved optimal by Pirl
(1969) [3]
Disk pack10.svg
11 ≈ 3.923...0.7148...Proved optimal by Melissen
(1994) [4]
Disk pack11.svg Disk pack11 2.svg
124.029...0.7392...Proved optimal by Fodor
(2000) [5]
Disk pack12.svg
13 ≈ 4.236...0.7245...Proved optimal by Fodor
(2003) [6]
Disk pack13.svg Disk pack13b.svg
144.328...0.7474...Conjectured optimal by Goldberg
(1971). [7]
Disk pack14.svg
15 ≈ 4.521...0.7339...Conjectured optimal by Pirl
(1969). [7]
Disk pack15.svg
164.615...0.7512...Conjectured optimal by Goldberg
(1971). [7]
Disk pack16.svg
174.792...0.7403...Conjectured optimal by Reis
(1975). [7]
Disk pack17.svg
18 ≈ 4.863...0.7609...Conjectured optimal by Pirl (1969),
with additional arrangements by Graham, Lubachevsky, Nurmela, and Östergård (1998). [7]
Disk pack18.svg Disk pack18 2.svg
Disk pack18 3.svg Disk pack18 8.svg
Disk pack18 4.svg Disk pack18 5.svg
Disk pack18 9.svg Disk pack18 10.svg
Disk pack18 6.svg Disk pack18 7.svg
19 ≈ 4.863...0.8032...Proved optimal by Fodor
(1999) [8]
Disk pack19.svg
205.122...0.7623...Conjectured optimal by Goldberg (1971). [7] Disk pack20.svg

Special cases

Only 26 optimal packings are thought to be rigid (with no circles able to "rattle"). Numbers in bold are prime:

Of these, solutions for n = 2, 3, 4, 7, 19, and 37 achieve a packing density greater than any smaller number > 1. (Higher density records all have rattles.) [9]

See also

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References

  1. Friedman, Erich, "Circles in Circles", Erich's Packing Center, archived from the original on 2020-03-18
  2. 1 2 R.L. Graham, Sets of points with given minimum separation (Solution to Problem El921), Amer. Math. Monthly 75 (1968) 192-193.
  3. 1 2 3 U. Pirl, Der Mindestabstand von n in der Einheitskreisscheibe gelegenen Punkten, Mathematische Nachrichten 40 (1969) 111-124.
  4. H. Melissen, Densest packing of eleven congruent circles in a circle, Geometriae Dedicata 50 (1994) 15-25.
  5. F. Fodor, The Densest Packing of 12 Congruent Circles in a Circle, Beiträge zur Algebra und Geometrie, Contributions to Algebra and Geometry 41 (2000) ?, 401–409.
  6. F. Fodor, The Densest Packing of 13 Congruent Circles in a Circle, Beiträge zur Algebra und Geometrie, Contributions to Algebra and Geometry 44 (2003) 2, 431–440.
  7. 1 2 3 4 5 6 Graham RL, Lubachevsky BD, Nurmela KJ, Ostergard PRJ. Dense packings of congruent circles in a circle. Discrete Math 1998;181:139–154.
  8. F. Fodor, The Densest Packing of 19 Congruent Circles in a Circle, Geom. Dedicata 74 (1999), 139–145.
  9. Sloane, N. J. A. (ed.). "SequenceA084644". The On-Line Encyclopedia of Integer Sequences . OEIS Foundation.