%I #19 Jan 01 2019 06:31:06
%S 1,3,54,1140,99051,13049563,6044482889,4738211572702,
%T 11986520595161863,54755153078468134960,764291947227525464744293,
%U 20119942924108379011391597989,1558052539448513320447263528275071,234788223520702255614480389250160811898,101199388044301804167035198499446336399419451,86918369741985767628242106496018767545685968221295
%N Number of ways to cover the n X n+1 grid graph by vertex disjoint cycles.
%H Andrew Howroyd, <a href="/A222203/b222203.txt">Table of n, a(n) for n = 2..24</a>
%H Peter Tittmann, <a href="http://web.archive.org/web/20070715034048/http://www.htwm.de/~peter/research/enumeration.html">Enumeration in graphs: counting Hamiltonian cycles</a> [Archived link]
%H Robert Israel, <a href="/A222203/a222203.pdf">The 54 solutions for n=4</a>
%Y Cf. A222202, A222204.
%K nonn
%O 2,2
%A _N. J. A. Sloane_, Feb 14 2013