%I #9 Mar 01 2020 20:44:40

%S 0,1,5,6,226,1072,255088,4638576,6663430912,467260456608,

%T 3916162476483538,1076226888605605706,51249820944023435573470,

%U 56126499620491437281263608,14870957102232406137455708164254,65882516522625836326159786165530572,95494789899510664733921727510895952184006

%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).

%F a(2n+1) = A181584(n). - _Andrew Howroyd_, Mar 01 2020

%Y Cf. A137932 (circumference of the (n-1) X (n-1) grid graph).

%Y Cf. A003763 (number of Hamiltonian cycles in the 2n X 2n grid graph).

%Y Cf. A181584 (number of longest cycles in the (2n+1) X (2n+1) grid graph).

%K nonn

%O 1,3

%A _Eric W. Weisstein_, Mar 25 2018

%E Terms a(9) and beyond from _Andrew Howroyd_, Mar 01 2020