title: How to write 2**n - 1 as a recursive function?
body: <p>I need a function that takes n and returns <strong>2<sup>n</sup> - 1</strong> . It sounds simple enough, but the function has to be recursive. So far I have just 2<sup>n</sup>:</p>
  
  <pre><code>def required_steps(n):
      if n == 0:
          return 1
      return 2 * req_steps(n-1)
  </code></pre>
  
  <p>The exercise states: "You can assume that the parameter n is always a positive integer and greater than 0"</p>