%I M4818 #21 Apr 27 2024 15:06:32
%S 1,0,0,-2,0,-12,2,-78,24,-548,228,-4050,2030,-30960,17670,-242402,
%T 152520,-1932000,1312844,-15612150,11297052,-127551884,97291026,
%U -1051478274,838994486,-8732657724,7246304736,-72983051674,62686156026,-613243234224,543146222970
%N Magnetization for 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 C. Domb, Ising model, in Phase Transitions and Critical Phenomena, vol. 3, ed. C. Domb and M. S. Green, Academic Press, 1974; p. 421.
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H C. Domb, <a href="/A007239/a007239.pdf">Ising model</a>, Phase Transitions and Critical Phenomena 3 (1974), 257, 380-381, 384-387, 390-391, 412-423. (Annotated scanned copy)
%H Shigeo Naya, <a href="https://doi.org/10.1143/PTP.11.53">On the Spontaneous Magnetizations of Honeycomb and Kagomé Ising Lattices</a>, Progress of Theoretical Physics, 11 (1954), 53-62.
%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>
%F G.f.: (1 - 16 * x^3 / ((1+3*x) * (1-x)^3))^(1/8) [Shigeo Naya]. - _Andrey Zabolotskiy_, Jun 01 2022
%F a(n) ~ (-1)^n * 3^n / (Gamma(1/8) * 2^(1/4) * n^(7/8)) * (1 - (-1)^n * sqrt(sqrt(2) - 1) * Gamma(1/8)^2 / (2^(13/4) * Pi * n^(1/4))). - _Vaclav Kotesovec_, Apr 27 2024
%t CoefficientList[Series[(1 - 16 * x^3 / ((1+3*x) * (1-x)^3))^(1/8), {x, 0, 30}], x] (* _Vaclav Kotesovec_, Apr 27 2024 *)
%Y Cf. A002928, A007206.
%K sign,easy
%O 0,4
%A _Simon Plouffe_
%E Offset changed, signs of terms changed, and more terms added by _Andrey Zabolotskiy_, Jun 01 2022