1. nextCollatz n
2.   | even n = div n 2
3.   | otherwise = n * 3 + 1
4.  
5. collatzCount c n
6.   | n == 1 = c
7.   | otherwise = collatzCount (c + 1) (nextCollatz n)
8.  
9. lengths = map (collatzCount 0) [1..30]
10.  
11. main = putStrLn $ show lengths