$\displaystyle a_1= \frac{2}{3}$\displaystyle a_1= \frac{2}{3}

$\displaystyle a_1= \frac{4}{9}$\displaystyle a_1= \frac{4}{9}

$\displaystyle a_1= \frac{3}{2}$\displaystyle a_1= \frac{3}{2}

$\displaystyle a_1= \frac{9}{4}$\displaystyle a_1= \frac{9}{4}