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 A002909 Low temperature energy function for square lattice. (Formerly M0035 N0009) 3
 2, 0, -8, -24, -72, -240, -896, -3640, -15688, -70512, -326968, -1553288, -7523520, -37026704, -184677536, -931655064, -4746324296, -24387839056, -126257024696, -658011767016, -3449826712952, -18183760406080, -96309365029424, -512340286827272 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 REFERENCES N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). M. F. Sykes and M. E. Fisher, Antiferromagnetic susceptibility of the plane square and honeycomb Ising lattices, Physica, 28 (1962), 919-938. LINKS Robert Israel, Table of n, a(n) for n = 0..1000 FORMULA G.f.: (1+x)/(1-x) + ((1-6*x+x^2)/(1-x^2))*Sum_{k>=0} (2*k)!^2 * (x*(1-x)^2/(1+x)^4)^k/k!^4. - Robert Israel, Nov 27 2017 a(n) ~ -2 * (1 + sqrt(2))^(2*n) / (Pi*n^2). - Vaclav Kotesovec, Nov 28 2017 MAPLE u:=v->((1+v^2)*(1-(2/Pi)*(1-6*v^2+v^4)*EllipticK(4*v*(1-v^2)/(1+v^2)^2)/(1+v^2)^2)/2*v): S:= series(u((1-v)/(1+v))/((1-v)/(1+v))^2, v, 101): seq(coeff(S, v, j), j=0..100, 2); # Sean A. Irvine, Nov 27 2017 CROSSREFS Sequence in context: A241682 A076687 A062134 * A118437 A134185 A013489 Adjacent sequences:  A002906 A002907 A002908 * A002910 A002911 A002912 KEYWORD sign AUTHOR EXTENSIONS More terms from Sean A. Irvine, Nov 27 2017 STATUS approved

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Last modified June 2 14:21 EDT 2020. Contains 334787 sequences. (Running on oeis4.)