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 A255981 #16 May 05 2016 10:54:42 %S A255981 3,5,8,12,17 %N A255981 a(n) = greatest number of edges in a simple polygon on an n X n grid with no two edges parallel. %C A255981 Worthy of consideration to introduce slopes in the math classroom. %C A255981 a(7) >= 23 and a(8) >= 29, see illustration in Links. %H A255981 Hiroaki Yamanouchi, <a href="/A255981/a255981.pdf">Examples</a> %H A255981 Giovanni Resta, <a href="/A255981/a255981.png">Illustration of a(7)>=23 and a(8)>=29</a> %e A255981 a(3) = 5 because of this quadrilateral in a 3 x 3 square: %e A255981 1 2 . %e A255981 . 4 . %e A255981 5 . 3 %e A255981 a(4) = 8 because of this polygon: %e A255981 1 3 . 4 %e A255981 . . 2 6 %e A255981 . . 5 7 %e A255981 . 8 . . %Y A255981 Cf. A271449. Construction perhaps related to construction of Costas arrays: A008404. %K A255981 nonn,more %O A255981 2,1 %A A255981 _Gordon Hamilton_, Mar 13 2015 %E A255981 a(5)-a(6) corrected by _Hiroaki Yamanouchi_, Mar 14 2015