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 A260318 #36 Mar 25 2022 20:31:00 %S A260318 1,0,0,1,1,0,0,0,0,0,0,4,4,0,0,32,64,0,0,240,352,0,0,1664,1632,0,0, %T A260318 16448,21888,0,0,203392,333952,0,0,2922752,4325376,0,0,38592000, %U A260318 50746368,0,0,630794240,897616896,0,0,10758713344,17514086400,0,0,203437559808,326022221824,0,0,4306790547456,6265275064320,0,0,97204813266944,145913049251840,0,0 %N A260318 Number of doubly symmetric characteristic solutions to the n-queens problem. %C A260318 The problem of placing eight queens on a chessboard so that no one of them can take any other in a single move is a particular case of the more general problem: On a square array of n X n cells place n objects, one on each of n different cells, in such a way that no two of them lie on the same row, column, or diagonal. %C A260318 There are no (interesting) doubly centrosymmetric solutions for n < 4, and there is just one complete set for n = 4: 2413, 3142 and one for n = 5: 25314, 41352. %C A260318 On the ordinary chessboard of 8 X 8 cells there are a total of 92 solutions, consisting of 11 sets of equivalent ordinary solutions and one set of equivalent symmetric solutions. There are no doubly symmetric solutions in this case. %D A260318 Maurice Kraitchik: Mathematical Recreations. Mineola, NY: Dover, 2nd ed. 1953, pp. 247-255 (The Problem of the Queens). %H A260318 P. Capstick and K. McCann, <a href="/A000170/a000170_1.pdf">The problem of the n queens</a>, apparently unpublished, no date (circa 1990?) [Scanned copy] %H A260318 M. A. Sainte-Laguë, <a href="https://eudml.org/doc/192551">Les Réseaux (ou Graphes)</a>, Mémorial des Sciences Mathématiques, Fasc. 18, Gauthier-Villars, Paris, 1923, 64 pages. See p. 47. %H A260318 M. A. Sainte-Laguë, <a href="/A002560/a002560.pdf">Les Réseaux (ou Graphes)</a>, Mémorial des Sciences Mathématiques, Fasc. 18, Gauthier-Villars, Paris, 1923, 64 pages. See p. 47. [Incomplete annotated scan of title page and pages 18-51] %F A260318 a(n) = A033148(n) / 2 for n >= 2. - _Don Knuth_, Jun 20 2017 %Y A260318 A002562 = A260318 + A260319 + A260320, A000170 = 2*A260318 + 4*A260319 + 8*A260320 (n>1). %K A260318 nonn,more %O A260318 1,12 %A A260318 _N. J. A. Sloane_, Jul 22 2015 %E A260318 More terms, due to _Don Knuth_, added by _Colin Barker_, Jun 20 2017