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 A386560 #8 Aug 02 2025 10:02:52 %S A386560 4,72,424,1396,3536,7292,14272,24332,39356,59920,91348,128084,182664, %T A386560 245804,323116,418552,547820,684680,869388,1060892,1289564,1560920 %N A386560 Place a point on the integer coordinates, up to |n|, along all four axial directions on a Cartesian plane, and then join an infinite straight line between every pair of points: a(n) is the number of finite regions created in the resulting graph. %H A386560 Scott R. Shannon, <a href="/A386560/a386560.png">Image for n = 1</a>. In this and other images the integer coordinates are highlighted as white dots while the outer open regions, which are not counted, are darkened. %H A386560 Scott R. Shannon, <a href="/A386560/a386560_1.png">Image for n = 2</a>. %H A386560 Scott R. Shannon, <a href="/A386560/a386560_2.png">Image for n = 3</a>. %H A386560 Scott R. Shannon, <a href="/A386560/a386560_3.png">Image for n = 4</a>. %H A386560 Scott R. Shannon, <a href="/A386560/a386560_4.png">Image for n = 5</a> %F A386560 a(n) = A386561(n) - A386559(n) + 1 by Euler's formula. %Y A386560 Cf. A386559 (vertices), A386561 (edges), A386562 (k-gons), A344993, A344857, A344279, A345459. %K A386560 nonn,more %O A386560 1,1 %A A386560 _Scott R. Shannon_, Jul 26 2025