Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%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