Suppose $n\geq 5$ and $f(x)$ is a polynomial of degree $n$, then in general $f(x)$ is not solvable by radicals, but there are certain special polynomials which are solvable by radicals. Is there a characterization of all such polynomials ?
Edit: Of course Galois group is solvable is one characterization, but I am looking for more stronger charaterization for some special values of $n$ (say $n=5$, or $n$ is prime), if not for general $n$.

