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 A018811 #16 Nov 29 2017 09:22:29 %S A018811 0,0,0,0,10,4,4,20,44,36,64,124,200,236,272,308,548,692,852,1108,1396, %T A018811 1452,1768,2116,2496,2908,3568,4292,5428,5956,6500,7444,8452,8980, %U A018811 10208,11516,13348,14700,16116,17596,20124,22476,24956,28092,31404,33052,36032 %N A018811 Number of lines through exactly 4 points of an n X n grid of points. %H A018811 Seiichi Manyama, <a href="/A018811/b018811.txt">Table of n, a(n) for n = 0..1000</a> %H A018811 S. Mustonen, <a href="http://www.survo.fi/papers/PointsInGrid.pdf">On lines and their intersection points in a rectangular grid of points</a> [From _Seppo Mustonen_, Apr 18 2009] %F A018811 a(n) = 1/2 (f(n, 5) - 2 f(n, 4) + f(n, 3)) where f(n, k) = Sum ((n - |kx|)(n - |ky|)); -n<kx<n, -n<ky<n, (x, y)=1. [From _Seppo Mustonen_, Apr 18 2009] %Y A018811 Cf. A119437. %K A018811 nonn %O A018811 0,5 %A A018811 _David W. Wilson_