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%I M1841 #20 Sep 19 2015 09:24:53
%S 0,2,8,24,64,156,358,786,1664,3434,6902,13656,26464,50772,95754,
%T 179442,331294,609496,1106106,2004852,3586874,6423028,11351274,
%U 20126538,35191190,61883196,107179834,187216848,321395596,558468104
%N Series for second perpendicular moment of square lattice (eventually changes sign).
%C The first negative term is the 66th.
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H I. Jensen, <a href="/A006730/b006730.txt">Table of n, a(n) for n = 0..171</a> (from Jensen link below)
%H J. W. Essam et al., <a href="http://dx.doi.org/10.1103/PhysRevB.33.1982">Analysis of extended series for bond percolation on the directed square lattice</a>, Phys. Rev. B 33 (1986), 1982-1986.
%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 (1988), 3815-3832.
%H I. Jensen, <a href="http://www.ms.unimelb.edu.au/~iwan/dirperc/series/sqbx2.ser">More terms</a>
%H Iwan Jensen, Anthony J. Guttmann, <a href="http://arxiv.org/abs/cond-mat/9509121">Series expansions of the percolation probability for directed square and honeycomb lattices</a>, J. Phys. A 28 (1995), no. 17, 4813-4833.
%Y Cf. A006461, A006727, A006728, A006729.
%K sign
%O 0,2
%A _N. J. A. Sloane_, _Simon Plouffe_