∵lnN=lgN/lge(对数换底公式)
且1/2ln2=1/2lg2/lge,1/3ln3=1/3lg3/lge,1/5lg5/lge
lg2<lg3<lg5.又∵1/2<1/3<1/5.∴1/2ln2<1/3ln3<1/5ln5.