f(n)=k,n是自然数,K是0.987651234658.的小数点后的第n位数字,如f(1)=9,f(2)=8,f(3)=7,求f(...f(f(5))...+f(...f(f(8))...).
问题描述：
f(n)=k,n是自然数,K是0.987651234658.的小数点后的第n位数字,如f(1)=9,f(2)=8,f(3)=7,
求f(...f(f(5))...+f(...f(f(8))...).
答
f(5)=5
f(...f(f(5))...=5
f(8)=3
f(f(8))=f(3)=7
fff8=f7=2
f(2)=8
f(...f(f(8))...).为每四个一个循环