Popular science blurb:
https://scitechdaily.com/descartes-unfinished-mystery-mathematicians-solve-380-year-old-geometry-problem/
Academic Paper:
“The classic Descartes circle theorem relates the curvatures of four mutually externally tangent circles, three “petal” circles around the exterior of a central circle, forming a “3-flower” configuration. We generalise this theorem to the case of an “n -flower”, consisting of n tangent circles around the exterior of a central circle, and give an explicit equation satisfied by their curvatures. The proof uses a spinorial description of horospheres in hyperbolic geometry.”