The nonrelativistic Bethe stopping power function contains the constant 2*pi*N*e^4 where N is Avogadro's number and e is the electron charge. In the literature, this constant is often calculated to be 78,500. If calculate the constant, I get 606,235 (=2 * pi * 6.02214179E+23 mol^-1 *(1.602176487E-19 C)^4). Does anybody know what my mistake is? Thank you.