an=Sn-S(n-1)=n^2(an)-(n-1)^2[a(n-1)](n+1)an=(n-1)a(n-1)3a2=a14a3=2a25a4=3a3.(n+1)an=(n-1)a(n-1)左右同时相加得到：a2+a3+a4+.+a(n-1)+(n+1)an=a1即：a1+a2+a3+.+an=2a1-n*an=sn=n^2an将a1=1代入并解出an得：an...