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 A120443 Number of (undirected) Hamiltonian paths in the n X n grid graph. 16
 1, 4, 20, 276, 4324, 229348, 13535280, 3023313284, 745416341496, 730044829512632, 786671485270308848, 3452664855804347354220, 16652005717670534681315580, 331809088406733654427925292528, 7263611367960266490262600117251524 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Jesper L. Jacobsen, Table of n, a(n) for n = 1..17 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. J.-M. Mayer, C. Guez and J. Dayantis, Exact computer enumeration of the number of Hamiltonian paths in small square plane lattices, Physical Review B, Vol. 42 Number 1, 1990. Eric Weisstein's World of Mathematics, Grid Graph Eric Weisstein's World of Mathematics, Hamiltonian Path FORMULA a(n) = A096969(n) / 2 for n > 1. EXAMPLE From Robert FERREOL, Apr 03 2019: (Start) a(3) = 20: there are 4 paths similar to   + - + - +           |   + - + - +   |   + - + - + 8 paths similar to   + - + - +   |       |   +   + - +   |   |   +   + - + and 8 paths similar to   + - + - +   |       |   +   +   +   |   |   |   +   + - + (End) CROSSREFS Main diagonal of A332307. Cf. A003685, A003695, A003778, A145402. Cf. A003763, A000532, A001184, A145157, A271507, A007764, A121785, A121789. Sequence in context: A222655 A000847 A188810 * A053400 A120599 A012797 Adjacent sequences:  A120440 A120441 A120442 * A120444 A120445 A120446 KEYWORD nonn,walk,changed AUTHOR David Bevan, Jul 19 2006 EXTENSIONS More terms from Jesper L. Jacobsen (jesper.jacobsen(AT)u-psud.fr), Dec 12 2007 STATUS approved

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Last modified February 18 15:30 EST 2020. Contains 332019 sequences. (Running on oeis4.)