Re-arrange, remove cruft and random primes

src/3n+1/Main.hs

@@ -6,6 +6,22 @@ https://youtu.be/094y1Z2wpJg
 import           Control.Monad ()
 import           Debug.Trace   (trace)
 
+main :: IO ()
+main = print $ take 100 $ map f [2^1000..]
+
+f :: Integer -> Integer
+f n = s 1 n
+  where
+    s :: Integer -> Integer -> Integer
+    s i n
+      | n ==    1  = i
+      | n ==    0  = i
+      | n ==  (-1) = i
+      | n ==  (-5) = i
+      | n == (-17) = i
+      | even n = s (succ i) (n `div` 2)
+      | odd  n = s (succ i) (3*n + 1)
+
 f' :: Integer -> Integer
 f' n = f'' 1 n
   where
@@ -22,25 +38,8 @@ f' n = f'' 1 n
             t'  = t'' $ trace ("END: " ++ show n ++ ", length: " <> show i) t''
             t'' = trace "\n#######################################################\n"
 
-f :: Integer -> Integer
-f n = s 1 n
-  where
-    s :: Integer -> Integer -> Integer
-    s i n
-      | n ==    1  = i
-      | n ==    0  = i
-      | n ==  (-1) = i
-      | n ==  (-5) = i
-      | n == (-17) = i
-      | even n = s (succ i) (n `div` 2)
-      | odd  n = s (succ i) (3*n + 1)
-
-main :: IO ()
-main = print $ map f [2^361..]
-
 -- collatz collect
 -- generate the collatz sequence and return it
-
 cc :: Integer -> [Integer]
 cc n = cc' [] n
   where
@@ -54,10 +53,3 @@ cc n = cc' [] n
       | even n = cc' acc' (n `div` 2)
       | odd  n = cc' acc' (3*n + 1)
       where acc' = acc <> [n]
-
-primes :: [Integer]
-primes = sieve [2..]
-  where
-    sieve (p:xs) = p : sieve [x|x <- xs, x `mod` p > 0]
-
-isPrime k = (k > 1) && null [ x | x <- [2..k - 1], k `mod` x == 0]