#### Answer

Next three terms: 128, 256, and 512
Formula:
$a_{1}$=4
$a_{n}$=$2a_{n-1}$

#### Work Step by Step

Looking at the problem, we see that neither addition nor subtraction will work since the numbers are getting exponentially bigger; therefore, we need to find a ratio of two terms, namely the second and first, third and second, third and fourth, etc...
We see $\frac{8}{4}$=2, then $\frac{16}{8}$=2, and $\frac{32}{16}$=2.
Through this, we see 2 is the constant number, or the number that is used to multiply the numbers in the sequence to gain the next value in the set.
We know $a_{1}$=4, then we need to find a formula for the next numbers in the set.
Since the next term is two times the previous term, the formula should be:
$a_{n}$=$2a_{n-1}$,
The next three terms are:
$64(2)=128
\\128(2)=256)
\\256(2) = 512$