See also:<p><a href="https://oeis.org/A250001/a250001_4.pdf" rel="nofollow">https://oeis.org/A250001/a250001_4.pdf</a>
PDF of all configurations for 4 circles<p><a href="https://www.youtube.com/watch?v=bRIL9kMJJSc">https://www.youtube.com/watch?v=bRIL9kMJJSc</a>
Numberphile video explaining the problem