Answer:
255
Step-by-step explanation:
A "perfect square" is where all 4 sides are the same. If the total area isn't able to divided by 4 and be a whole number, or if it doesn't multiply into itself, then it is "imperfect."
All the other numbers are able to be divided by 4 and be a whole number. Or at least be able to be multiplied into itself with numbers divisible by 4. However nothing multiply's into 255 as well as being divisible by 4.
