Data commit

Task/Giuga-numbers/Haskell/giuga-numbers.hs

@@ -0,0 +1,20 @@
+--for obvious theoretical reasons the smallest divisor of a number bare 1
+--must be prime
+primeFactors :: Int -> [Int]
+primeFactors n = snd $ until ( (== 1) . fst ) step (n , [] )
+ where
+  step :: (Int , [Int] ) -> (Int , [Int] )
+  step (n , li) = ( div n h , li ++ [h] )
+   where
+    h :: Int
+    h = head $ tail $ divisors n --leave out 1
+
+divisors :: Int -> [Int]
+divisors n = [d | d <- [1 .. n] , mod n d == 0]
+
+isGiuga :: Int -> Bool
+isGiuga n = (divisors n /= [1,n]) && all (\i -> mod ( div n i - 1 ) i == 0 )
+ (primeFactors n)
+
+solution :: [Int]
+solution = take 4 $ filter isGiuga [2..]