
\documentclass[11pt]{article}
\usepackage[francais]{babel}
\usepackage{multirow}
\usepackage{mathtools}
\pagestyle{empty}
\begin{document}

\[      
\renewcommand\arraystretch{1.4}
%
\begin{array}{|c|c||c|c|}
 \hline
 \multirow{2}{0.5cm}{$k$} & 
 \multirow{2}{0.5cm}{$p_G$} &
 \multicolumn{2}{c|}{test} \\
 \cline{3-4}
 & & \text{DADWRD} & \text{RARWRD} \\
 \hline
 2 & 1     & 90n   & 228 n \\
 3 & p_d   & 202 n & 449 n \\
 4 & p_d^2 & 424 n & 891 n \\
 5 & p_d^3 & 866 n & 1774 n \\
 \hline
\end{array}
\]
\end{document}
