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 A045673 #15 Sep 13 2019 22:48:20
%S A045673 0,1,4,9,12,16,24,25,28,33,36,40,49,52,57,60,64,72,73,76,81,84,88,96,
%T A045673 97,100,105,108,112,121,124,129,136,144,145,148,153,156,160,168,169,
%U A045673 172,177,180,184,192,193,196,201,204,216,217,220,225,228,232
%N A045673 Curvatures in diagram constructed by inscribing 2 circles of curvature 0 and 1 inside circle of curvature 0, continuing indefinitely to inscribe circles wherever possible.
%C A045673 Appears to be a superset of {A008784 - 1}. - _Ralf Stephan_, Jan 26 2005
%C A045673 See A189226 for additional comments, references, links, examples, and crossrefs. - _Jonathan Sondow_, Aug 24 2012
%H A045673 K. E. Stange, <a href="http://arxiv.org/abs/1208.4836">The sensual Apollonian circle packing</a>, arXiv:1208.4836 [math.NT], 2012-2014; see section 14. - _Jonathan Sondow_, Aug 24 2012
%Y A045673 Cf. A042944-A042946, A045679, A189226.
%K A045673 nonn
%O A045673 0,3
%A A045673 _Allan Wilks_