%I M1839 #17 Oct 04 2019 07:40:55
%S 0,2,8,24,60,136,288,582,1132,2138,3940,7114,12632,22080,38160,65056,
%T 110172,184032,306968,503650,831408,1340338,2201840,3479116,5733312,
%U 8814468,14772040,21734370,37997724,51650456,98952836,115227474,266750996,223323542,768153044,261658998,2443777216,-717803658,8754481712,-8229926352,35018197920,-51106610852
%N Series for second perpendicular moment of square 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="/A006734/b006734.txt">Table of n, a(n) for n = 0..158</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/sqsx2.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.
%K sign
%O 0,2
%A _N. J. A. Sloane_, _Simon Plouffe_