当n=1时,可知S1=a1=1/3.当n>1时,因为Sn=n（2n-1）anSn-1=(n-1)[2(n-1)-1]an-1由于 Sn-Sn-1=an可知 n（2n-1）an-（n-1)[2(n-1)-1]an-1=an化简得 an=[(2n-3)/(2n+1)]an-1an-1=[(2n-5)/(2n-1)]an-2an-2=[(2n-7）/（2n-3...