Add implementations with filter for prime functions

prime.hs

@@ -1,5 +1,8 @@
 -- Exercice from slide 42/82
 
 dividers n = [k | k <- [2..(n-1)], rem n k == 0]
+dividersf n = filter (\k -> rem n k == 0) [2..(n-1)]
 
 primer n = [i | i <- [2..(n-1)], null (dividers i)]
+primerf n = filter (\i -> null (dividersf i)) [2..(n-1)]
+