Disk covering problem $r(20)$
The smallest value $r(20)$ such that $20$ disks of radius $r(20)$ can be arranged to cover the unit disk.
Lower bound:
Unknown
Upper bound:
${\approx}0.271$
Updates
-
2018
Upper bound: ${\approx}0.271$
Jeremy Tan in 2018
[via Circles Covering Circles, Erich Friedman]