This is a standard FA design..
When we say FA , it is taken to be as an NFA..
So for nth bit from the right to be '1' , no of states in minimal NFA = n + 1
As far as number of states in minimal DFA is concerned , it is 2n..
One question came on the same topic this yr and I did a mistake ; wrote the number of states considering NFA while the question asked about minimal DFA..