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%I M4838 #16 Nov 20 2017 13:59:33
%S 12,48,180,792,3444,15000,64932,280200,1204572,5159448,22043292,
%T 93952428,399711348,1697721852,7200873444,30500477676,129049335924,
%U 545436439536,2303305856916
%N Number of self-avoiding walks on hexagonal lattice, with additional constraints.
%C The hexagonal lattice is the familiar 2-dimensional lattice in which each point has 6 neighbors. This is sometimes called the triangular lattice.
%C The extra constraint here is that the next to "middle" points of the walk must be adjacent in the lattice. Exact details are in the Redner paper. - _Sean A. Irvine_, Nov 20 2017
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H G. Nebe and N. J. A. Sloane, <a href="http://www.math.rwth-aachen.de/~Gabriele.Nebe/LATTICES/A2.html">Home page for hexagonal (or triangular) lattice A2</a>
%H S. Redner, <a href="http://physics.bu.edu/~redner/pubs/pdf/jpa13p3525.pdf">Distribution functions in the interior of polymer chains</a>, J. Phys. A 13 (1980), 3525-3541, doi:10.1088/0305-4470/13/11/023.
%Y Cf. A007201.
%K nonn,walk
%O 2,1
%A _Simon Plouffe_
%E a(15)-a(20) from _Sean A. Irvine_, Nov 20 2017
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