Each successive number is divided by 3.
[tex]\dfrac{486}3=162[/tex]
[tex]\dfrac{162}3=54[/tex]
[tex]\dfrac{54}3=18[/tex]
and so on. The next number in the sequence is [tex]\dfrac{18}3=6[/tex], and in general, you have a geometric sequence defined recursively by
[tex]\begin{cases}a_1=486\\\\a_n=\dfrac13a_{n-1}&\text{for }n>1\end{cases}[/tex]
and a closed form
[tex]a_n=\dfrac13a_{n-1}=\left(\dfrac13\right)^2a_{n-2}=\cdots=\left(\dfrac13\right)^{n-1}a_1=\dfrac{486}{3^{n-1}}[/tex]
