%I M0186 #8 Mar 30 2012 16:44:58
%S 1,0,-1,-2,-2,0,2,4,3,0,-1,6,28,72,139,242,407,722,1215,2348,3753,
%T 7186,9558,21800,16576,61234,-7978,226136,-446034,1118180,-3180033,
%U 6428640,-24607343,56904504
%N Percolation series for directed square lattice.
%D R. J. Baxter and A. J. Guttmann, Series expansion of the percolation probability for the directed square lattice, J. Phys. A 21 (1988), 3193-3204.
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%Y Cf. A006461.
%K sign
%O 0,4
%A _N. J. A. Sloane_.