If a₁, a₂, a₃, _ _ _ _ _, a₉ are in GP, then what is the value of the following determinant?

$\left| {\begin{array}{*{20}{c}} {{ln\:a_1}}&{{ln\:a_2}}&{{ln\:a_3}}\\ {{ln\:a_4}}&{{ln\:a_5}}&{{ln\:a_6}}\\ {{ln\:a_7}}&{{ln\:a_8}}&{{ln\:a_9}} \end{array}} \right|$

Let $A = \left| {\begin{array}{*{20}{c}} p&q\\ r&s \end{array}} \right|$

where p, q, r and s are any four different prime numbers less than 20. What is the maximum value of the determinant?