In Step 1, we have 4 dots. Therefore: f(1)=4
In Step 2, we have 16 dots. Therefore: f(2)=16
In Step 3, we had 64 dots. Therefore: f(3)=64
We observe that each of the f(n) is 4 raised to the particular n.
[tex]\begin{gathered} f(1)=4^1=4 \\ f(2)=4^2=16 \\ f(3)=4^3=64 \end{gathered}[/tex]Therefore, the next term is obtained through the multiplication of the previous term by 4.
Therefore, the recursive formula which fits the dot will be:
[tex]f(n)=f(n-1)\cdot4,\text{ f(1)=4}[/tex]