Answer
$\qquad \displaystyle \sum_{n=1}^{\infty}6^{n}$
Work Step by Step
From the first four terms, we observe the pattern
nth term = $6^{n}$.
The first term corresponds to n=1 (lower limit).
The sum has infinitely many terms (no upper limit ... we write $\infty$)
Summation notation:$\qquad \displaystyle \sum_{n=1}^{\infty}6^{n}$
