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 A151943 #24 Jul 31 2021 07:50:11 %S A151943 1,6,21,36,55,80,108,140 %N A151943 Maximal number of moves required for the 2 X n generalization of the sliding block 15-puzzle (or fifteen-puzzle). %C A151943 See A087725 for more about this problem and its history. See also A151944. %C A151943 Three corrections to table III of the Korf reference: the radius of the 2 X 4 should be 36; the depth of the 3 X 5 should be 52, and the ratio of the 3 X 5 should be 14.379. - _Tomas Rokicki_, Aug 17 2011 %H A151943 Richard Korf, <a href="https://www.cs.helsinki.fi/u/bmmalone/heuristic-search-fall-2013/Korf2008.pdf">Linear-time Disk-Based Implicit Graph Search</a>, Journal of the ACM 55 (2008), No. 6. %H A151943 Anton Kulchitsky, <a href="/A087725/a087725.txt">Comments on the Fifteen Puzzle</a> %H A151943 Tomas Rokicki, <a href="http://forum.cubeman.org/?q=node/view/238">Twenty-Four puzzle, some observations</a>, 2011 %F A151943 From _Ben Whitmore_, Jul 31 2021: (Start) %F A151943 a(n) = 2*n^2 + O(n*log(n)). %F A151943 a(n) >= 2*n^2 - n. %F A151943 (End) %K A151943 nonn,hard,more %O A151943 1,2 %A A151943 Anton Kulchitsky (kulchits(AT)arsc.edu), Aug 14 2009, Aug 16 2009 %E A151943 a(7)-a(8) from Table III of Richard Korf's work by _Tomas Rokicki_, Aug 17 2011