(n+1)^2a(n+1)-n^2a(n)=a(n+1)+a(n)+...+a(1)-[a(n)+...+a(1)]=a(n+1),(n+2)na(n+1)=n^2a(n),(n+2)a(n+1)=na(n),(n+2)(n+1)a(n+1)=n(n+1)a(n),{n(n+1)a(n)}是首项为1*2a(1)=2a(1),的常数列.n(n+1)a(n)=2a(1),a(n)=2a(1)/[n(n+1)]
