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 A386561 #7 Aug 02 2025 10:02:28 %S A386561 8,136,804,2608,6568,13396,26556,45120,73060,110984,171144,238900, %T A386561 344212,462788,607384,786476,1037772,1293904,1654432,2013768,2447312, %U A386561 2965392 %N A386561 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 edges created in the resulting graph. %C A386561 See A386559 and A386560 for images of the graphs. %F A386561 a(n) = A386559(n) + A386560(n) - 1 by Euler's formula. %Y A386561 Cf. A386559 (vertices), A386560 (regions), A386562 (k-gons), A347751, A344899, A344896, A345650. %K A386561 nonn,more %O A386561 1,1 %A A386561 _Scott R. Shannon_, Jul 26 2025