This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A121603 #7 Aug 13 2020 14:25:50 %S A121603 2,3,4,5,6,7,8,9,11 %N A121603 Numbers n such that the radius of the smallest circle into which n unit circles can be packed is 1 + csc(Pi/k), where k >= 2 is an integer. %C A121603 Corresponding k values are in A121604. For these n, the centers of k unit circles can form a regular k-gon with sides of length 2 centered at the center of the larger circle. From the diagrams in the link it appears likely that 13,18,19 are the next three terms. %H A121603 E. Friedman, <a href="https://erich-friedman.github.io/packing/cirincir/">Erich's Packing Center: "Circles in Circles"</a> %e A121603 See A121602 for the case n=11 involving a 9-gon. %Y A121603 Cf. A121604, A121570, A121598, A121601, A121602. %K A121603 nonn %O A121603 1,1 %A A121603 _Rick L. Shepherd_, Aug 09 2006