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%I #9 Jan 01 2019 06:52:00
%S 1,1,2,6,14,154,1072,5320,301384,4638576,49483138,13916993782,
%T 467260456608,10754797724124,14746957510647992,1076226888605605706,
%U 53540340738182687296,354282765498796010420944,56126499620491437281263608,6040964455632840415885507728,191678405883294971709423926242394,65882516522625836326159786165530572
%N Write n=3i+j, 0<=j<3; a(n) = number of Hamiltonian cycles on square grid of points of size 2i+2 X 2i+2 (if j=0), 2i+2 X 2i+3 (j=1) or 2i+3 X 2i+4 (j=2).
%C An interleaving of A003763 and A222200.
%H Peter Tittmann, <a href="http://www.htwm.de/~peter/research/enumeration.html">Enumeration in graphs: counting Hamiltonian cycles</a> [Broken link?]
%H Peter Tittman, <a href="/A222200/a222200.jpg">Illustration of a(4) = 14</a> [Taken from preceding link]
%H Peter Tittmann, <a href="http://web.archive.org/web/20101127064650/https://www.staff.hs-mittweida.de/~peter/research/enumeration.html">Enumeration in graphs: counting Hamiltonian cycles</a> [Backup copy of top page only, on the Internet Archive]
%H <a href="/index/Gra#graphs">Index entries for sequences related to graphs, Hamiltonian</a>
%Y Cf. A003763, A222200.
%K nonn
%O 0,3
%A _N. J. A. Sloane_, Feb 14 2013