  The one-dimensional SU$(n)$ Hubbard model is investigated numerically for
$n=2,3,4$, and 5 at half filling and $1/n$ filling using the density-matrix
renormalization-group (DMRG) method. The energy gaps and various quantum
information entropies are calculated. In the half-filled case, finite spin and
charge gaps are found for arbitrary positive $U$ if $n > 2$. Furthermore, it is
shown that the transition to the gapped phase at $U_{\rm c}=0$ is of
Kosterlitz-Thouless type and is accompanied by a bond dimerization both for
even and odd $n$. In the $1/n$-filled case, the transition has similar features
as the metal-insulator transition in the half-filled SU(2) Hubbard model. The
charge gap opens exponentially slowly for $U>U_{\rm c}=0$, the spin sector
remains gapless, and the ground state is non-dimerized.
