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 A384702 #17 Jun 15 2025 14:36:43 %S A384702 0,1,37,245,1205,4213,12261,29742,65507,130824,245325,432262,727259 %N A384702 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 (finite) regions created. %C A384702 The infinite exterior region is not counted. %H A384702 Scott R. Shannon, <a href="/A384702/a384702.jpg">Image for a(3) = 37</a>. %H A384702 Scott R. Shannon, <a href="/A384702/a384702_1.jpg">Image for a(4) = 245</a>. %H A384702 Scott R. Shannon, <a href="/A384702/a384702_2.jpg">Image for a(5) = 1205</a>. %F A384702 a(n) = A384703(n) - A384701(n) + 1 by Euler's formula, for n > 1. %Y A384702 Cf. A384700 (circles), A384701 (vertices), A384703 (edges), A359570, A374826, A374337, A372978. %K A384702 nonn,more %O A384702 1,3 %A A384702 _Scott R. Shannon_ and _N. J. A. Sloane_, Jun 07 2025