当n≥2时 Sn=lgn Sn-1=lg(n-1) Sn-Sn-1=an=lgn-lg(n-1)=lg[n/(n-1)] 当n=1时S1=a1=0不属于an=lg[n/(n-1)] n=1时a1=0 n≥2时an=an=lg[n/(n-1)]
