Hmm... why does this function ends in an infinite loop when evaluating for any integer > 3?
smallestMultiple n = factors [2..n] where
factors [] = []
factors (h:xs) = h:(factors $ filter ((<)1) [div x h|x<-xs])
where
div x y
|x `mod` y ==0 = x `div` y
|otherwise = x
It appears that the main problem is that you define a local version of div:
div x y
| x `mod` y == 0 = x `div` y
| otherwise = x
Since bindings in where clauses (as well as in let) are recursive, the div on the right hand side of the first case refers to the same div you're defining! You can fix this by using a different name, like div':
div' x y
| x `mod` y == 0 = x `div` y
| otherwise = x
