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%I M2020 #27 Oct 05 2019 09:15:19
%S 2,12,46,144,402,1040,2548,5992,13632,30220,65486,139404,291770,
%T 602908,1229242,2482792,4959014,9836840,19323246,37773464,73182570,
%U 141345292,270647584,517513972,980893354
%N Series for second perpendicular 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="/A006742/b006742.txt">Table of n, a(n) for n = 1..82</a>
%H I. G. Enting, A, J. Guttmann and I. Jensen, <a href="http://dx.doi.org/10.1088/0305-4470/27/21/014">Low-Temperature Series Expansions for the Spin-1 Ising Model</a>, J. Phys. A. 27 (21) (1994) 6987-7006. <a href="http://arXiv.org/abs/hep-lat/9410005">[arxiv:hep-lat/9410005]</a>
%H J. W. Essam, A. J. Guttmann and K. De'Bell, <a href="http://dx.doi.org/10.1088/0305-4470/21/19/018">On two-dimensional directed percolation</a>, J. Phys. A 21 (19) (1988), 3815-3832.
%H I. Jensen, <a href="https://researchers.ms.unimelb.edu.au/~ij@unimelb/dirperc/series/triasite_t1.ser">More terms</a>
%H Iwan Jensen, Anthony J. Guttmann, <a href="http://dx.doi.org/10.1088/0305-4470/28/17/015">Series expansions of the percolation probability for directed square and honeycomb lattices</a>, 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 sign
%O 1,1
%A _N. J. A. Sloane_, _Simon Plouffe_
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