What? Quadratic means 'squared'. Where are you getting x4 from?
"f(x) scales quadratically with x" means, in a rough sense, that f(2x) is about four times as large as f(x), and f(5x) is about twenty-five times as large as f(x).
Which is what the hashing problem O(n^2) is about.
So "4 times" = x
4 by your logic?
You do know that the relationship 5x : 25 is actually 5
2?
The way it is now, the amount of processing needed scales quadratically, i.e. to the fourth power every step change.