factor n divisor
  | (divisor >= n-1 || n == 1) = [n]
  | rem n divisor == 0 =  (factor (n `div` divisor) 2) ++ (factor divisor 2)
  | otherwise = factor n (divisor+1)

mymax [] acc = acc
mymax (x:xs) acc
	| x > acc = mymax xs x
	| otherwise = mymax xs acc

e3 = mymax (factor 600851475143 2) 0