Packing $15$ unit circles in an equilateral triangle
OwOUwUOwU, via Wikimedia Commons. CC BY-SA 4.0.
The side length of the smallest equilateral triangle into which $15$ unit circles can be packed.
Value: $8+2\sqrt{3}$ (≈11.4641)
Updates
-
Upper bound: $8+2\sqrt{3}$
(≈11.4641)
Reference unknown
[via Circles in Triangles, Erich Friedman] -
1961
Lower bound: $8+2\sqrt{3}$
(≈11.4641)
Erdős and Groemer in 1961
[via Circles in Triangles, Erich Friedman]