1,6,5,7,2,8,6,9()括号中填啥呢?

问题描述:

1,6,5,7,2,8,6,9()括号中填啥呢?

答案是3
a(n)=a(n-1)-a(n-2) n=2k,k>0
5=6-1
2=7-5
6=8-2
()=9-6