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.
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: