Numerical evidence suggests: -6n+12 A603[n]+A605[n]-8 A604[n]-5 = 0 sage: uniq([-6*n+12*A603[n]+1*A605[n]-8*A604[n]-5 for n in [ 1 .. 499]]) [0] A603 Number of nonnegative solutions to x^2 + y^2 <= n^2 A604 Number of nonnegative solutions to x^2 + y^2 + z^2 <= n^2 A605 Number of points of norm <= n in cubic lattice