{\displaystyle S(x):=\left\{{\begin{array}{ll}-{\frac {1}{2\pi }}\ln |x|\ ,&n=2\ ,\\{\frac {1}{(n-2)\omega _{n}}}{\frac {1}{\|x\|^{n-2}}}\ ,&n\geq 3\ ,\\\end{array}}\right.}