设数列{an}的前n项和为Sn,如果a1=6/7,an=3Sn/(n+3),那么a48=书上给的答案是350,但把S1代入,不符合题意,如果该数列是分段数列,求出来的结果是an=3（n+2）（n+1）/28,a48=525/2,请问答案是否是这样?

Answer 1

根据题意：Sn=(n+3)xan/3∵Sn+1=(n+4)xan+1/3an+1=Sn+1-Sn3xan+1=(n+4)xan+1-(n+3)xanan+1=(n+3）/(n+1)an=(n+3）/(n+1)x(n+2）/(n)x(n+1）/(n-1)xn/(n-2)……x6/4x5/3x4/2xa1=（n+3)x(n+2)/2x3xa1得出n=47a48=50x49...