(n+1)a(n+1)=nan
a(n+1)/an=n/(n+1)
a(n+1)/an=n/(n+1)
.
a3/a2=2/3
a2/a1=1/2
以上等式相乘得
a(n+1)/a1=1/(n+1)
a(n+1)/a1=1/(n+1)
a(n+1)=1/(n+1)
an=1/n