由an+1=an+ln(1+1/n)知an=a(n-1)+ln(1+1/n-1).an=a(n-1)+ln(1+1/n-1)an-1=a(n-2)+ln(1+1/n-2)...a2=a1+ln(1+1/1)上述等式两边相加,得an=a1+ln(1+1/n-1)+ln(1+1/n-2)+...+ln(1+1/1)=2+ln(1+1/n-1)(1+1/n-2)...(1+1/1)=2+ln[n/(n-1)*(n-1)/(n-2)...2/1]=2+lnn