How to work out the list of wirth numbers using haskell

Question

Hello I'm (battling) to learn Haskell. Please help solve this problem using Haskell and list comprehension.

Consider the list of numbers wirth defined as follows:

(i) 1 is a member of wirth.

(ii) If x is a member of wirth, then so are 2 × x + 1 and 3 × x + 1.

(iii) These are the only elements of wirth.

Give a definition of wirth which produces the elements in increasing order.

(Source: Haskell Exercises 4: ZF-expressions Antoni Diller 26 July 2011)

Here is my Haskell attempt

f l = f ([2*u+1 | u <- l ] ++ [3*u+1 | u <- l])

Which seems to produce an infinite loop. This never returns

take 1 (f [1])

I managed to solve this problem using C# both iteratively and recursively.

private static List<int> WirthIterative(int take)
{

  var done = new List<int>();
  var todo = new Queue<int>();
  todo.Enqueue(1);

  int count = 0;

  while (todo.Count > 0 && count < take)
  {
    count++;

    var next = todo.Dequeue();

    var a = 2 * next + 1;
    var b = 3 * next + 1;

    todo.Enqueue(a);
    todo.Enqueue(b);

    done.Add(next);
  }

  done.Sort();
  return done;

}


private static List<int> WirthRecursive(int take)
{
  var result = new List<int>();
  _WirthRecursive(1, 0);
  result.Sort();
  return result;

  void _WirthRecursive(int member, int i)
  {
    if (i >= take) { return; }
    var a = 2 * member + 1;
    var b = 3 * member + 1;
    _WirthRecursive(a, i + 1);
    _WirthRecursive(b, i + 1);
    result.Add(member);
  }
}