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 A307454 #13 Apr 22 2019 11:46:43 %S A307454 1,3,9,33,123,513,2077,8759,37184,159508,688446,2993451,13082724 %N A307454 a(n) is the number of canonical polygons with 2n edges having 2-fold rotational symmetry. %H A307454 Lars Blomberg, <a href="/A307454/a307454.pdf">Examples of canonical polygons with 2-fold rotational symmetry</a> %Y A307454 Cf. A052436, A307387, A307391, A307426, A307454, A307455, A307456, A307519. %K A307454 nonn,more %O A307454 2,2 %A A307454 _Lars Blomberg_, Apr 09 2019