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 A374826 #14 Jul 22 2024 09:50:20 %S A374826 1,2,6,16,80,324,1666,3120,17703,28780,115401,96624,528073,589708 %N A374826 Place n equally spaced points on the circumference of a circle of radius r and then connect each pair of points with straight lines whose intersections create A007569(n) - n additional points. Draw a circle of radius r around each of the A007569(n) points. The sequence gives the total number of regions formed from all circle intersections. %H A374826 Scott R. Shannon, <a href="/A374826/a374826.jpg">Image for n = 2</a>. In this and other images the starting circles' centers are shown as white dots. %H A374826 Scott R. Shannon, <a href="/A374826/a374826_1.jpg">Image for n = 3</a>. %H A374826 Scott R. Shannon, <a href="/A374826/a374826_2.jpg">Image for n = 4</a>. %H A374826 Scott R. Shannon, <a href="/A374826/a374826_3.jpg">Image for n = 5</a>. %H A374826 Scott R. Shannon, <a href="/A374826/a374826_4.jpg">Image for n = 6</a>. %H A374826 Scott R. Shannon, <a href="/A374826/a374826_5.jpg">Image for n = 8</a>. %H A374826 Scott R. Shannon, <a href="/A374826/a374826_6.jpg">Image for n = 10</a>. %F A374826 a(n) = A374827(n) - A374825(n) + 1, by Euler's formula. %Y A374826 Cf. A374825 (vertices), A374827 (edges), A374828 (k-gons), A007569 (total circles), A093005, A374337. %K A374826 nonn,more %O A374826 1,2 %A A374826 _Scott R. Shannon_, Jul 21 2024