documentclass{beamer}
usepackage[utf8]{inputenc}
usepackage[T1]{fontenc}
usepackage{blkarray, bigstrut}

begin{document}

begin{frame}
[ bigstrutjot=5pt
X = begin{blockarray}{*{7}{c}}
& 1 & 2 & dots & j & dots &n \
  begin{block}{r[*{6}{c}]}%
    1 & & & & & & bigstrut[t]\
    2 & & & & & & \
    vdots & & & & & & \
    i & & & & & & \
    vdots & & & & & & \
    m & & & & & & bigstrutjot = 3ptbigstrut[b]\
  end{block}
  end{blockarray} ]
end{frame}

end{document}