IMathAS-libretexts

\displaystyle {r}={1.5}

\displaystyle {L}_{{n}}={1.5}\cdot{L}_{{{n}-{1}}}

\displaystyle {f}_{{0}}={4200}

\displaystyle {L}_{{n}}={4200}\cdot{1.5}^{{n}}

\displaystyle {f}_{{19}}={9310718.844223}

\displaystyle {f}_{{26}}={159082360.25247}