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 A271449 #6 May 05 2016 10:54:35 %S A271449 0,3,6,9,12,18 %N A271449 Greatest number of edges in a simple polygon on an n X n grid with no two edges parallel or perpendicular. %C A271449 a(8) >= 22, see picture in Links. %H A271449 Giovanni Resta, <a href="/A271449/a271449.png">Illustration of a(3)-a(7) and a(8) >= 22</a> %e A271449 a(5)=9 because of this polygon on a 5 X 5 grid: %e A271449 2 . . . . %e A271449 . . 1 3 5 %e A271449 . . 4 . 7 %e A271449 . 6 . . 8 %e A271449 9 . . . . %e A271449 See Links for other examples. %Y A271449 Cf. A255981. %K A271449 nonn,more %O A271449 2,2 %A A271449 _Giovanni Resta_, May 05 2016