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 A064941 #15 Apr 19 2016 02:13:58 %S A064941 1,3,26,596,38171,7083827,3852835452,6200587517574,29752897658253125, %T A064941 427721252609771505989,18479976131829456895423324, %U A064941 2405174963192312814001570260392,944597040906414962273553855513194341,1120924326970482645724785944664901286951323 %N A064941 Quartering a 2n X 2n chessboard (reference A257952) considering only the 90-deg rotationally symmetric results (omitting results with only 180-deg symmetry). %H A064941 Walter Gilbert, <a href="https://web.archive.org/web/20070624190323/http://www.otal.umd.edu/~walt/misc/Checkerboard.htm">Chessboard quartering</a>; includes generating program. %F A064941 No formula known. However, the subset of solutions consisting of "tiles" with minimum edge lengths from a corner of the board to the center is A001700. %F A064941 This sequence can be computed by counting paths in a graph. To compute the n-th term a graph with n X (n-1) vertices is required. Each graph vertex corresponds to 4 intersections between grid lines on the chessboard and graph edges correspond to ways of cutting the board along the grid lines. Frontier (matrix-transfer) graph path counting methods can then be applied to the graph to get the actual count. - _Andrew Howroyd_, Apr 18 2016 %Y A064941 Cf. A257952, A113900. %K A064941 nonn %O A064941 1,2 %A A064941 Walter Gilbert (Walter(AT)Gilbert.net), Oct 28 2001 %E A064941 a(7)-a(8) from _Juris Cernenoks_, Feb 27 2013 %E A064941 a(9)-a(14) from _Andrew Howroyd_, Apr 18 2016