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 A261596 #15 Sep 15 2015 15:34:30 %S A261596 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,2,4,6,1,3,5,2,5,1,4,7,3,6,3,5,2,8,1,7, %T A261596 4,6,2,4,9,7,5,3,1,6,8,2,4,6,8,10,1,3,5,7,9 %N A261596 Triangular array T(n, k) read by rows (n >= 1, 1 <= k <= n): row n gives the lexicographically earliest symmetric characteristic solution to the n queens problem, or n zeros if no symmetric characteristic solution exists. The k-th queen is placed in square (k, T(n, k)). %C A261596 See the comments under A260319. %D A261596 Maurice Kraitchik: Mathematical Recreations. Mineola, NY: Dover, 2nd ed. 1953, p. 247-255 (The Problem of the Queens). %e A261596 1 <= n < 6: no symmetric solutions exist. %e A261596 n = 6: 246135 is the first and only symmetric solution. %e A261596 .*.... %e A261596 ...*.. %e A261596 .....* %e A261596 *..... %e A261596 ..*... %e A261596 ....*. %e A261596 n = 7: 2514736 is the first of two existing symmetric solutions. %e A261596 n = 8: 35281746 is the first and only symmetric solution. %e A261596 Triangle starts: %e A261596 0; %e A261596 0, 0; %e A261596 0, 0, 0; %e A261596 0, 0, 0, 0; %e A261596 0, 0, 0, 0, 0; %e A261596 2, 4, 6, 1, 3, 5; %e A261596 2, 5, 1, 4, 7, 3, 6; %e A261596 3, 5, 2, 8, 1, 7, 4, 6; %e A261596 ... %Y A261596 Cf. A141843, A260319, A261595, A261597. %K A261596 nonn,tabl %O A261596 1,16 %A A261596 _Martin Renner_, Aug 25 2015