Disk covering problem $r(25)$
The smallest value $r(25)$ such that $25$ disks of radius $r(25)$ can be arranged to cover the unit disk.
Lower bound:
Unknown
Upper bound:
$\frac{1}{\sqrt{6}+\sqrt{3}}$
(≈0.2391463)
Updates
-
2018
Upper bound: $\frac{1}{\sqrt{6}+\sqrt{3}}$
(≈0.2391463)
Jeremy Tan in 2018
[via Circles Covering Circles, Erich Friedman]