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 A237429 #19 Jun 30 2023 10:27:02 %S A237429 0,1,19,1394,281990,377205809,1539951848735,44222409563201991, %T A237429 3842818845468254120853,2396657968905952750257244144 %N A237429 Number of nonisomorphic Hamiltonian cycles on 2n X 2n square grid of points with exactly one axis of reflective symmetry. %H A237429 Ed Wynn, <a href="http://arxiv.org/abs/1402.0545">Enumeration of nonisomorphic Hamiltonian cycles on square grid graphs</a>, arXiv:1402.0545 [math.CO], 2014. %F A237429 a(n) = A227257(n) - A237430(n). %e A237429 The following two cycles with n=3 are counted only once, since they are isomorphic under the full symmetry group of the square. They have a horizontal and a vertical axis respectively. No example has a diagonal axis, since this brings other symmetries (see A063524). %e A237429 o-o-o-o-o-o o-o o-o o-o %e A237429 | | | | | | | | %e A237429 o o-o-o-o-o o o o o o o %e A237429 | | | | | | | | %e A237429 o o-o-o-o-o o o o o o o %e A237429 | | | | | | | | %e A237429 o o-o-o-o-o o o o o o o %e A237429 | | | | | | | | %e A237429 o o-o-o o-o o o-o o-o o %e A237429 | | | | %e A237429 o-o-o-o-o-o o-o-o-o-o-o %Y A237429 Cf. A209077, A227257, A237430. %K A237429 nonn,walk,more %O A237429 1,3 %A A237429 _Ed Wynn_, Feb 07 2014