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%I M1379 #17 Oct 04 2019 07:41:57
%S 1,0,0,-1,-2,-5,-10,-20,-41,-86,-182,-393,-853,-1887,-4208,-9445,
%T -21350,-48612,-111307,-255236,-590543,-1362919,-3182137,-7362611,
%U -17377129,-40125851,-96106251,-219681825,-539266908,-1200140540
%N Percolation series for directed 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="/A006836/b006836.txt">Table of n, a(n) for n = 0..35</a> (from link below)
%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>, J. Phys. A 21 (1988), 3815-3832.
%H I. Jensen, <a href="https://researchers.ms.unimelb.edu.au/~ij@unimelb/dirperc/series/triasite_pp.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>
%Y Cf. A006739.
%K sign
%O 0,5
%A _N. J. A. Sloane_.
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