\begin{table}%t2
\caption{\label{P1-2tabla}Coefficients  $a_{r} {(i,j)}$ and $ b_{r} {(i,j)}$ of
  the power series for $r$, corresponding to a stratified medium with
  a $\frac{\rho_{\rm c}}{(1+\frac{Z}{H})^{2}}$ law of density distribution in altitude.}
\par
\begin{tabular}{c c l l}
\hline \hline 
${i}$  &  ${j}$  &  $a_{r} {(i,j)}$     & $ b_{r} {(i,j)}$  \\ 
\hline
  1     &  1  &  1  &  2 \\
\hline
  2 & 1 & --2 & --16  \\
    & 2 & --6 &  --24  \\
\hline 
  3 & 1 & 16   & 272 \\
    & 2 & 120   &  960  \\
    & 3 & 120  & 720   \\
\hline 
  \end{tabular}
\end{table}