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 A261595 #19 Sep 16 2015 03:47:42 %S A261595 1,0,0,0,0,0,2,4,1,3,2,5,3,1,4,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, %T A261595 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 %N A261595 Triangular array T(n, k) read by rows (n >= 1, 1 <= k <= n): row n gives the lexicographically earliest doubly centro-symmetric characteristic solution to the n queens problem, or n zeros if no doubly centro-symmetric characteristic solution exists. The k-th queen is placed in square (k, T(n, k)). %C A261595 See the comments under A260318. %D A261595 Maurice Kraitchik: Mathematical Recreations. Mineola, NY: Dover, 2nd ed. 1953, pp. 247-255 (The Problem of the Queens). %e A261595 n = 1: 1 is the trivial solution. %e A261595 2 <= n < 4: no doubly centro-symmetric solutions exist. %e A261595 n = 4: 2413 is the first and only solution. %e A261595 .*.. %e A261595 ...* %e A261595 *... %e A261595 ..*. %e A261595 n = 5: 25314 is the first and only solution. %e A261595 6 <= n < 12: no doubly centro-symmetric solutions exist. %e A261595 Triangle starts: %e A261595 1; %e A261595 0, 0; %e A261595 0, 0, 0; %e A261595 2, 4, 1, 3; %e A261595 2, 5, 3, 1, 4; %e A261595 0, 0, 0, 0, 0, 0; %e A261595 ... %Y A261595 Cf. A141843, A260318, A261596, A261597. %K A261595 nonn,tabl %O A261595 1,7 %A A261595 _Martin Renner_, Aug 25 2015