%I
%S 0,1,5,6,226,1072,255088,4638576
%N Number of longest cycles in the n X n grid graph.
%C a(10) = 467260456608.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/GraphCycle.html">Graph Cycle</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/GridGraph.html">Grid Graph</a>
%F a(2n) = A003763(n).
%Y Cf. A137932 (circumference of the (n1) X (n1) grid graph).
%Y Cf. A003763 (number of Hamiltonian cycles in the 2n X 2n grid graph).
%K nonn
%O 1,3
%A _Eric W. Weisstein_, Mar 25 2018
