NeumannO(n, z) = piecewise | 1/z | n = 0 1/4 ( sum_(k=0)^floor(n/2) ((n - k - 1)! (z/2)^(2 k - n - 1))/(k!)) n | otherwise for (NeumannO(0, z) = 1/z and NeumannO(1, z) = 1/z^2 and NeumannO(2, z) = (4 + z^2)/z^3 and NeumannO(3, z) = (3 (8 + z^2))/z^4 and NeumannO(4, z) = (192 + 16 z^2 + z^4)/z^5 and n element Z and n>=0)