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 A211172 #15 Feb 16 2025 08:33:17 %S A211172 6,5,7,3,4,2,1,9,8,9,8,1,5,6,7,4,3,2,3,2,4,8,9,1,6,5,7,5,7,6,2,3,4,9, %T A211172 8,1,8,1,9,7,5,6,3,2,4,2,4,3,1,8,9,5,7,6,7,6,5,4,2,3,8,1,9,1,9,8,6,7, %U A211172 5,2,4,3,4,3,2,9,1,8,7,6,5 %N A211172 A Sudoku torus. %C A211172 The sequence is a listing for a Sudoku grid: %C A211172 6 5 7 3 4 2 1 9 8 %C A211172 9 8 1 5 6 7 4 3 2 %C A211172 3 2 4 8 9 1 6 5 7 %C A211172 5 7 6 2 3 4 9 8 1 %C A211172 8 1 9 7 5 6 3 2 4 %C A211172 2 4 3 1 8 9 5 7 6 %C A211172 7 6 5 4 2 3 8 1 9 %C A211172 1 9 8 6 7 5 2 4 3 %C A211172 4 3 2 9 1 8 7 6 5 %C A211172 No two diagonally adjacent elements are the same. If the grid is rolled into a cylinder either way, this is still true making a 'Sudoku torus'. %C A211172 This extra information can be used to construct puzzles that use 'no diagonal' logic. %C A211172 The two lexicographical Sudoki in the cross-references have one internal diagonal each and several external diagonals. %H A211172 Mathworld, <a href="https://mathworld.wolfram.com/Sudoku.html">Sudoku</a> %H A211172 Wikipedia, <a href="http://en.wikipedia.org/wiki/Sudoku">Sudoku</a> %e A211172 If a puzzle has say: %e A211172 |x %e A211172 5| %e A211172 ___|x %e A211172 then x cannot be 5. %Y A211172 Cf. A107739. %Y A211172 Cf. A114288, A112454 (lexicographic grids). %K A211172 nonn,fini,full,tabf %O A211172 1,1 %A A211172 _Jon Perry_, Jan 31 2013