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 A005160 M0396 #21 Aug 23 2023 10:39:32 %S A005160 1,0,1,2,3,0,12,40,100,0,1225,6860,28812,0,1037232,9779616 %N A005160 Number of alternating sign n X n matrices invariant under a quarter turn. %C A005160 Robbins incorrectly gives a(12) = 6460. %D A005160 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %D A005160 R. P. Stanley, A baker's dozen of conjectures concerning plane partitions, pp. 285-293 of "Combinatoire Enumerative (Montreal 1985)", Lect. Notes Math. 1234, 1986. %H A005160 G. Kuperberg, <a href="https://arxiv.org/abs/math/0008184">Symmetry classes of alternating-sign matrices under one roof</a>, arXiv:math/0008184 [math.CO], 2000-2001. %H A005160 D. P. Robbins, <a href="https://arxiv.org/abs/math/0008045">Symmetry classes of alternating sign matrices</a>, arXiv:math/0008045 [math.CO], 2000. %H A005160 R. P. Stanley, <a href="/A005130/a005130.pdf">A baker's dozen of conjectures concerning plane partitions</a>, pp. 285-293 of "Combinatoire Enumerative (Montreal 1985)", Lect. Notes Math. 1234, 1986. Preprint. [Annotated scanned copy] %F A005160 Robbins gives a simple (conjectured) formula. %Y A005160 a(4n) gives A059476. %K A005160 nonn,nice,more %O A005160 1,4 %A A005160 _N. J. A. Sloane_