OFFSET
0,3
LINKS
Hendrik A. Kramers and Gregory H. Wannier. Statistics of the two-dimensional ferromagnet. Part I. Phys. Rev. 60 (1941), 252-262.
Hendrik A. Kramers and Gregory H. Wannier. Statistics of the two-dimensional ferromagnet. Part II. Phys. Rev. 60 (1941), 263-276. See (45), p. 264.
Hendrik A. Kramers and Gregory H. Wannier, Extract 1 from page 264 of Part II.
Hendrik A. Kramers and Gregory H. Wannier, Extract 2 from page 264 of Part II.
Gandhimohan M. Viswanathan, The hypergeometric series for the partition function of the 2D Ising model, J. Stat. Mech. (2015) P07004; arXiv:1411.2495 [cond-mat.stat-mech], 2014-2015.
Wikipedia, Square lattice Ising model.
FORMULA
From Vaclav Kotesovec, Apr 28 2024: (Start)
a(n) ~ -c * 16^n / n^2, where c = 0.071286406...
Conjecture: c = exp(2*G/Pi)/(8*Pi) = 0.071286406674269408358123..., where G is the Catalan's constant A006752. (End)
MATHEMATICA
CoefficientList[Exp[-x HypergeometricPFQ[{1, 1, 3/2, 3/2}, {2, 2, 2}, 16 x]] + O[x]^20, x] (* Andrey Zabolotskiy, Mar 10 2024, using the g. f. from Gandhimohan M. Viswanathan *)
CROSSREFS
KEYWORD
sign,easy
AUTHOR
N. J. A. Sloane, Mar 10 2024
EXTENSIONS
Terms a(6) and beyond from Andrey Zabolotskiy, Mar 10 2024
STATUS
approved