%I #3 Mar 30 2012 16:49:38
%S 1,0,4,-4,12,-20,40,-68,124,-208,352,-580,944,-1508,2392,-3732,5772,
%T -8836,13396,-20132,30024,-44412,65240,-95188,137984,-198808,284816,
%U -405764,575072,-810980,1138184,-1590132,2211868,-3063740,4226640,-5808372,7952204,-10848196,14747560
%N G.f. = { 1+sum(4*n*q^n, n=1..infinity)} / { theta series for square lattice }.
%e 1 + 4*q + 8*q^2 + 12*q^3 + 16*q^4 + 20*q^5 + 24*q^6 + 28*q^7 + ... / 1 + 4*q + 4*q^2 + 4*q^4 + 8*q^5 + 4*q^8 + 4*q^9 + 8*q^10 + 8*q^13 + ... = 1 + 4*q^2 - 4*q^3 + 12*q^4 - 20*q^5 + 40*q^6 - 68*q^7 + 124*q^8 - 208*q^9 + ...
%K sign
%O 0,3
%A _N. J. A. Sloane_, Feb 21 2003