The following picture shows an example of a dashed disk of radius 1 covered by six solid-line disks of radius ~0.6. One of the covering disks is placed central and the remaining five in a symmetrical way around it.
While this is not the best layout for r(6), similar arrangements of six, seven, eight, and nine disks around a central disk all having same radius result in the best layout strategies for r(7), r(8), r(9), and r(10), respectively.3 The corresponding angles θ are written in the "Symmetry" column in the above table.
Kershner, Richard (1939), "The number of circles covering a set", American Journal of Mathematics, 61 (3): 665–671, doi:10.2307/2371320, JSTOR 2371320, MR 0000043. /wiki/Doi_(identifier) ↩
Friedman, Erich. "Circles Covering Circles". Retrieved 4 October 2021. https://erich-friedman.github.io/packing/circovcir/ ↩