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 A307455 #11 Apr 22 2019 11:46:40 %S A307455 1,0,2,2,1,7,6,28,27,107,94,488,386,2066,1630,8392,6780,34962,28056, %T A307455 147356,117621,622558,500525,2657666,2149374 %N A307455 a(n) is the number of canonical polygons with n edges having exactly 1 line of reflection symmetry. %C A307455 For n even, the symmetry line passes through two opposite vertices, or cuts through two opposite edges. For n odd it passes through one vertex and cuts the opposite edge. That explains the even-odd irregularity in the sequence. %H A307455 Lars Blomberg, <a href="/A307455/a307455.pdf">Examples of canonical polygons with exactly 1 line of reflection symmetry</a> %Y A307455 Cf. A052436, A307387, A307391, A307426, A307454, A307455, A307456, A307519. %K A307455 nonn,more %O A307455 3,3 %A A307455 _Lars Blomberg_, Apr 09 2019