%I M4603 #30 Jun 18 2022 08:42:00
%S 0,9,18,-306,-3240,49176,1466640,-13626000,-1172668032,75256704,
%T 1392243773184,18426692664576,-2213592367094784
%N High temperature series for spin-1/2 Heisenberg specific heat on 2D 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 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H G. A. Baker Jr., H. E. Gilbert, J. Eve, and G. S. Rushbrooke, <a href="https://doi.org/10.1016/0375-9601(67)90860-2">On the two-dimensional, spin-1/2 Heisenberg ferromagnetic models</a>, Phys. Lett., 25A (1967), 207-209.
%H N. Elstner, R. R. P. Singh and A. P. Young, <a href="https://doi.org/10.1103/PhysRevLett.71.1629">Finite temperature properties of the spin-1/2 Heisenberg antiferromagnet on the triangular lattice</a>, Phys. Rev. Lett., 71 (1993), 1629-1632.
%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>
%H J. Oitmaa and E. Bornilla, <a href="https://doi.org/10.1103/PhysRevB.53.14228">High-temperature-series study of the spin-1/2 Heisenberg ferromagnet</a>, Phys. Rev. B, 53 (1996), 14228.
%H <a href="/index/Sp#specific_heat">Index entries for sequences related to specific heat</a>
%Y Cf. A005399, A005402.
%K sign,more
%O 1,2
%A _N. J. A. Sloane_
%E Better description from _Steven Finch_
%E a(11)-a(12) added from Oitmaa and Bornilla by _Andrey Zabolotskiy_, Oct 20 2021
%E a(13) from Elstner et al. (see table I; signs differ because they consider antiferromagnet, and they mention energy instead of specific heat because the same coefficients are involved, cf. Eqs. (11) and (13) from Oitmaa & Bornilla) added by _Andrey Zabolotskiy_, Jun 17 2022