已知等差数列,已知等差数列{an}满足a2=3,a5=9,若数列{bn}满足b1=3,b下标(n+1)=a下标bn,则{bn}的通项公式

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已知等差数列,已知等差数列{an}满足a2=3,a5=9,若数列{bn}满足b1=3,b下标(n+1)=a下标bn,则{bn}的通项公式
已知等差数列,已知等差数列{an}满足a2=3,a5=9,若数列{bn}满足b1=3,b下标(n+1)=a下标bn,则{bn}的通项公式

已知等差数列,已知等差数列{an}满足a2=3,a5=9,若数列{bn}满足b1=3,b下标(n+1)=a下标bn,则{bn}的通项公式
a2=3,a5=9,
所以,d=(9-3)/3=2
a1=a2-d=1
an=2n-1
b[n+1]=a[bn]=2b[n]-1
b[n+1]-1=2b[n]-2=2(b[n]-1)
又因为b1-1=2
可知{b[n]-1}是首项为2,公比为2的等比数列
b[n]-2=2^n
b[n]=2^n+1

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