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 A290865 #17 Mar 07 2020 11:26:00 %S A290865 0,1,3,7,15,30,56,98,161,250,370,536,748,1027,1379,1807,2320,2954, %T A290865 3702,4604,5652,6852,8239,9858,11683,13748,16086,18700,21604,24887, %U A290865 28471,32491,36907,41751,47080,52876,59105,65965,73440,81521,90176 %N A290865 a(n) = number of regions in the configuration A290447(n). %H A290865 David Applegate, <a href="/A290865/b290865.txt">Table of n, a(n) for n = 1..100</a> %H A290865 M. F. Hasler, <a href="/A290447/a290447.html">Interactive web page for drawing the illustration for a(n).</a> %H A290865 N. J. A. Sloane (in collaboration with Scott R. Shannon), <a href="/A331452/a331452.pdf">Art and Sequences</a>, Slides of guest lecture in Math 640, Rutgers Univ., Feb 8, 2020. Mentions this sequence. %e A290865 With 3 points, there are 3 semicircles above the baseline, which bound a(3) = 3 regions. With 4 points, there are 6 semicircles, defining 7 regions (use the Halser webpage with n = 3 and 4). - _N. J. A. Sloane_, Aug 12 2017 %Y A290865 Cf. A290447, A290866, A290867, A332723 (number of regions with k edges). %Y A290865 See also A290876. %K A290865 nonn %O A290865 1,3 %A A290865 _David Applegate_, Aug 12 2017