explizit

a_n<4;6;9;13,5;...> explizit

$\begin{array}{rcll} a_2 &=& 6\\ a_3 &=& 9\\ a_4 &=& 13,5\\\\ q &=& \frac{a_2}{a_1} = \frac{a_3}{a_2}= \frac{a_4}{a_3} = 1.5\\\\ a_n &=& a_1\cdot q^{n-1} \\\\ \mathbf{a_n} & \mathbf{=} & \mathbf{ 4\cdot 1.5^{n-1} } \end{array}$