title: Calculate max combination of regex language
body: <p>This isn't really a coding question, but hopefully it is within the guide lines. I have a given language <code>L*</code> where <code>L = {pi,po}</code>. </p>
  
  <p>The question is how many combination I can make with <code>L*</code> where the maximum length is 9.</p>
  
  <p>The answer is 31, but i do not know how it got calculated. How is this calculated?</p>
  
  <p>If I should not ask this question here please inform me and I will remove the question.</p>