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 A003763 Number of (undirected) Hamiltonian cycles on 2n X 2n square grid of points. 42
 1, 6, 1072, 4638576, 467260456608, 1076226888605605706, 56126499620491437281263608, 65882516522625836326159786165530572, 1733926377888966183927790794055670829347983946, 1020460427390768793543026965678152831571073052662428097106 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Orientation of the path is not important; you can start going either clockwise or counterclockwise. The number is zero for a 2n+1 X 2n+1 grid (but see A222200). These are also called "closed rook tours". REFERENCES F. Faase, On the number of specific spanning subgraphs of the graphs G X P_n, Ars Combin. 49 (1998), 129-154. LINKS Artem M. Karavaev and N. J. A. Sloane, Table of n, a(n) for n=1..13 [First 11 terms from Artem M. Karavaev, Sep 29 2010; a(12) and a(13) from Pettersson, 2014, added by N. J. A. Sloane, Jun 05 2015] F. Faase, On the number of specific spanning subgraphs of the graphs G X P_n, Preliminary version of paper that appeared in Ars Combin. 49 (1998), 129-154. J. L. Jacobsen, Exact enumeration of Hamiltonian circuits, walks and chains in two and three dimensions, J. Phys. A: Math. Theor. 40 (2007) 14667-14678 Artem M. Karavaev, Hamilton Cycles. Ville H. Pettersson, Enumerating Hamiltonian Cycles, The Electronic Journal of Combinatorics, Volume 21, Issue 4, 2014. Ville Pettersson, Graph Algorithms for Constructing and Enumerating Cycles and Related Structures, Dissertation, Aalto, Finland, 2015. A. Pönitz, Computing invariants in graphs of small bandwidth, Mathematics in Computers and Simulation, 49(1999), 179-191 A. Pönitz, Über eine Methode zur Konstruktion... PhD Thesis (2004) C.3. T. G. Schmalz, G. E. Hite and D. J. Klein, Compact self-avoiding circuits on two-dimensional lattices, J. Phys. A 17 (1984), 445-453. N. J. A. Sloane, Illustration of a(2) = 6 Peter Tittmann, Enumeration in graphs: counting Hamiltonian cycles [Broken link?] Peter Tittmann, Enumeration in graphs: counting Hamiltonian cycles [Backup copy of top page only, on the Internet Archive] Eric Weisstein's World of Mathematics, Grid Graph Eric Weisstein's World of Mathematics, Hamiltonian Cycle Ed Wynn, Enumeration of nonisomorphic Hamiltonian cycles on square grid graphs, arXiv preprint arXiv:1402.0545 [math.CO], 2014. FORMULA a(n) = A321172(2n,2n). - Robert FERREOL, Apr 01 2019 EXAMPLE a(1) = 1 because there is only one such path visiting all nodes of a square. CROSSREFS Other enumerations of Hamiltonian cycles on a square grid: A120443, A140519, A140521, A222200, A222201. Sequence in context: A004806 A282233 A125536 * A179853 A268043 A190351 Adjacent sequences: A003760 A003761 A003762 * A003764 A003765 A003766 KEYWORD nonn,walk AUTHOR Jeffrey Shallit, Feb 14 2002 EXTENSIONS Two more terms from Andre Poenitz [André Pönitz] and Peter Tittmann (poenitz(AT)htwm.de), Mar 03 2003 a(8) from Herman Jamke (hermanjamke(AT)fastmail.fm), Nov 21 2006 a(9) and a(10) from Jesper L. Jacobsen (jesper.jacobsen(AT)u-psud.fr), Dec 12 2007 STATUS approved

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