[Tex/LaTex] Customising counter within enumerate-list

#enumeratelistsnumbering

Please consider the following code. I would like to use the enumerate-environment to generate a list, which (for better understanding) I built with the tabular-environment. I would like to have the second item labeled as "2-5.".

\documentclass[fontsize=12pt, paper=a4]{scrartcl}

\usepackage[T1]{fontenc}
\usepackage[latin1]{inputenc}
\usepackage{ngerman}

\begin{document}

\begin{enumerate}
\item bla
\item bla bla
\item bla bla bla
\end{enumerate}

\begin{table}[htbp]
\begin{tabular}{rl}
1. & bla \\
2-5. & bla bla   \\
6. & bla bla bla  \\
\end{tabular}
\end{table}

\end{document}


If you want to resume the numbering after a modification

\documentclass[fontsize=12pt, paper=a4]{scrartcl}

\usepackage[T1]{fontenc}
\usepackage[latin1]{inputenc}
\usepackage{ngerman}

\begin{document}
\begin{enumerate}
\item bla \stepcounter{enumi}
\item[\theenumi--5.] bla bla \setcounter{enumi}{5}
\item bla bla bla
\end{enumerate}
\end{document}


Thanks to egreg and Mico for the correction/modification!