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%I M4269 #21 Oct 04 2019 07:41:39
%S 0,6,60,314,1240,4166,12600,35324,93576,236944,578764,1371478,3169380,
%T 7165478,15901324,34705018,74661832,158529158,332756408,691084378,
%U 1421836528,2899678894,5867341452,11784640984,23512608484
%N Series for second parallel moment of hexagonal lattice.
%C The hexagonal lattice is the familiar 2-dimensional lattice in which each point has 6 neighbors. This is sometimes called the triangular lattice.
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H I. Jensen, <a href="/A006741/b006741.txt">Table of n, a(n) for n = 0..82</a> (from link below)
%H I. G. Enting, A, J. Guttmann and I. Jensen, <a href="https://arxiv.org/abs/hep-lat/9410005">Low-Temperature Series Expansions for the Spin-1 Ising Model</a>, J. Phys. A. 27 (1994) 6987-7006.
%H J. W. Essam, A. J. Guttmann and K. De'Bell, <a href="https://doi.org/10.1088/0305-4470/21/19/018">On two-dimensional directed percolation</a>, arXiv:hep-lat/9410005, 1994; J. Phys. A 21 (1988), 3815-3832.
%H I. Jensen, <a href="https://researchers.ms.unimelb.edu.au/~ij@unimelb/dirperc/series/triasite_t2.ser">More terms</a>
%H Iwan Jensen, Anthony J. Guttmann, <a href="https://arxiv.org/abs/cond-mat/9509121">Series expansions of the percolation probability for directed square and honeycomb lattices</a>, arXiv:cond-mat/9509121, 1995; J. Phys. A 28 (1995), no. 17, 4813-4833.
%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>
%K nonn
%O 0,2
%A _N. J. A. Sloane_, _Simon Plouffe_
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