As the quantum number increases, the difference of energy between consecutive energy levels:

Total energy for n th level =−13.6n2eV E2−E1=−13.614−11 =13.6×34=0.75×13.6eV E3−E2=−13.619−14 =13.6×536=0.14×13.6eV E4−E3=−13.6116−19 =13.6×7144eV=0.05×13.6eVObviously, the difference of energy between consecutive energy levels decreases.