已知数列{an}满足,a1=5,anan+1=2n,则a7a3等于______.

问题描述:

已知数列{an}满足,a1=5,anan+12n,则

a7
a3
等于______.

∵a1=5,anan+12n,∴5a221,∴a2=

2
5

同理,a3=10,a4=
4
5
,a5=20,a6=
8
5
,a7=40,
a7
a3
40
10
=4,
故答案为:4
答案解析:利用a1=5,anan+12n,计算出前7项,即可得到结论.
考试点:数列递推式.
知识点:本题考查数列递推式,考查学生的计算能力,属于基础题.