This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A002909 M0035 N0009 #29 Nov 29 2020 02:34:13
%S A002909 2,0,-8,-24,-72,-240,-896,-3640,-15688,-70512,-326968,-1553288,
%T A002909 -7523520,-37026704,-184677536,-931655064,-4746324296,-24387839056,
%U A002909 -126257024696,-658011767016,-3449826712952,-18183760406080,-96309365029424,-512340286827272
%N A002909 Low temperature energy function for square lattice.
%D A002909 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D A002909 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A002909 Robert Israel, <a href="/A002909/b002909.txt">Table of n, a(n) for n = 0..1000</a>
%H A002909 M. F. Sykes and M. E. Fisher, <a href="https://doi.org/10.1016/0031-8914(62)90080-0">Antiferromagnetic susceptibility of the plane square and honeycomb Ising lattices</a>, Physica, 28 (1962), 919-938.
%F A002909 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
%F A002909 a(n) ~ -2 * (1 + sqrt(2))^(2*n) / (Pi*n^2). - _Vaclav Kotesovec_, Nov 28 2017
%p A002909 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):
%p A002909 S:= series(u((1-v)/(1+v))/((1-v)/(1+v))^2,v,101):
%p A002909 seq(coeff(S,v,j),j=0..100,2); # _Sean A. Irvine_, Nov 27 2017
%t A002909 Table[SeriesCoefficient[(1 + v)/(1 - v)^3 ((1 - v)^2 + 2/Pi (1 - 6 v + v^2) EllipticK[(16 v^2)/(1 - v)^4]), {v, 0, k}], {k, 0, 100}] (* _Jan Mangaldan_, Nov 28 2020 *)
%K A002909 sign
%O A002909 0,1
%A A002909 _N. J. A. Sloane_
%E A002909 More terms from _Sean A. Irvine_, Nov 27 2017