hbar = 1.054571 (10^(-34)) (* J.s *)
k = 8.987551 (10^9)(* N.(m^2)/(C^2) *)
me = 9.109383 (10^(-31)) (* kg *)
e = 1.602176 (10^(-19)) (* C *)

a0 = ((hbar^2)/(me k (e^2)))

E0 = ((k (e^2))/(2a0)) (* J *)

EoinEV = E0/ e

1/e

{EoinEV/4,EoinEV/9,EoinEV/16}