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 A307391 #16 Apr 22 2019 11:46:26 %S A307391 2,0,2,2,8,14,62,196,892,3788,18098,86302,427340,2136248 %N A307391 a(n) is the number of canonical polygons with 4n edges containing only right angles. %C A307391 It appears that for the same sequence of angles there is one solution with all straight edges and one with all diagonal edges, so all terms are even. %H A307391 Lars Blomberg, <a href="/A307391/a307391.pdf">Examples of canonical polygons containing only right angles</a> %Y A307391 Cf. A052436, A307387, A307391, A307426, A307454, A307455, A307456, A307519. %K A307391 nonn,more %O A307391 1,1 %A A307391 _Lars Blomberg_, Apr 18 2019