Disk covering problem $r(19)$
The smallest value $r(19)$ such that $19$ disks of radius $r(19)$ can be arranged to cover the unit disk.
Lower bound:
Unknown
Upper bound:
$\frac{\sqrt{13}}{13}$
(≈0.2773501)
Updates
-
2018
Upper bound: $\frac{\sqrt{13}}{13}$
(≈0.2773501)
Jeremy Tan in 2018
[via Circles Covering Circles, Erich Friedman]