determining if a int is a power

[ddekker6 at chello.nl]

hello all,

im new to haskell and have to do some excersises. Well i ran into this problem. I have to determin if a list of int's contains a int that is a power. So i have been trying using "any" with a helper function which return a Bool if the int is a power and applying that to the list. I think that this aproach should work.
Anyway the problem im having is in the helper function. I have been trying this:
isPower n = 
	let powerF = floor(sqrt(n)) in
     	if (powerF*PowerF == n)
		then True
		else False
but this doesnt work. Prelude says that the definition of isPower needs a fractional int (if i remember correctly)  anyway it looks like something is wrong with my type's? Could you guys help me out? Is there a simple standard function i overlooked. Or what should i change? Thanks in advance guys/gals