$\sum_{n=1}^{\infty} \frac{5}{4^n}$

$\sum_{n=1}^{\infty} \left(\frac{2}{3}\right)^n$

$\sum_{n=0}^{\infty} \frac{1 + 2 \cdot 3^n}{4^n}$

$\sum_{n=1}^{\infty} \frac{1}{n \cdot 2^n}$