If f(a)=a^2 and a is a positive integer, which of the following CANNOT be the value of f(f(a))?
Choose the correct choice from the following.
A) 256
B) 16
C) 81
D) 1
E) 165
f(a)=a^2   f(f(a)) = (a^2)^2 = a^4   Therefore f(f(a)) will be numbers that are 4th power of other numbers.   Checking the options:   1 = 1^$   16 = 2^4   81 = 3^4   165. This cannot be written as the 4th power of any number   256 = 4^4   Answer: 165
<result>E</result>
If f(a)=a^2 and a is a positive integer, which of the following CANNOT be the value of f(f(a))?