this language accept all string except 'a'.
i.e. ((a)^p)* = {(a^2)*, (a^3)*, (a^5)*...... so on}
which is equal to { (aa)*, (aaa)*, (aaaaa)* ..........}
hence, create directly a dfa which accept all stings except 'a' OR create a dfa of only accepting 'a' and then take complement of it.
hence needs 3 state.