%I
%S 1,6,21,36,55,80,108,140
%N Maximal number of moves required for the 2 X n generalization of the sliding block 15puzzle (or fifteenpuzzle).
%C See A087725 for more about this problem and its history. See also A151944.
%C Three corrections to table III of the Korf reference: the radius of the 2x4 should be 36; the depth of the 3x5 should be 52, and the ratio of the 3x5 should be 14.379. [Tomas Rokicki, Aug 17 2011]
%D Richard Korf, Lineartime DiskBased Implicit Graph Search, Journal of the ACM 55 (2008), No. 6
%H Anton Kulchitsky, <a href="/A087725/a087725.txt">Comments on the Fifteen Puzzle</a>
%H Tomas Rokicki, Comments on <a href="http://forum.cubeman.org/?q=node/view/238">TwentyFour puzzle, some observations</a>
%K nonn,hard,more
%O 1,2
%A Anton Kulchitsky (kulchits(AT)arsc.edu), Aug 14 2009, Aug 16 2009
%E Extended the sequence for 2x7 and 2x8 from Table III of Richard Korf's work.
