We first intend to take the input in the form of binary numbers, since in finite automata, we deal with sequences rather than the number as a whole.

For 2, we use 10 Therefore, $log_2 2=1$, which is represented as 01

For 4, we use 100 Therefore, $log_24=2$, which is represented as 10

Hence, we find that the logic remains in erasing some additional 0 trailing after the 1.

We consider the input 16

16 in binary is 10000

$Log_2{16} = 4$

To obtain 4, we would have to erase the last two 0’s in 10000

Hence, we would be left with 100, which in decimal is 4, which is the required answer.