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 A384703 #9 Jun 15 2025 14:36:12 %S A384703 0,4,54,416,2182,7884,23294,56982,126310,253564,477462,844524,1424316 %N A384703 On a 2 X n grid of vertices, draw a circle through every unordered triple of non-collinear vertices: a(n) is the number of distinct edges in the planar graph formed from the intersections of the circles. %C A384703 The edges being counted are of course arcs of circles. %H A384703 Scott R. Shannon, <a href="/A384703/a384703.jpg">Image for a(3) = 54</a>. %F A384703 a(n) = A384701(n) + A384702(n) - 1 by Euler's formula, for n > 1. %Y A384703 Cf. A384700 (circles), A384701 (vertices), A384702 (regions), A359571, A374827, A374339, A373108. %K A384703 nonn,more %O A384703 1,2 %A A384703 _Scott R. Shannon_ and _N. J. A. Sloane_, Jun 07 2025