title: How to match digits between strings not between numbers
body: <p>Is it possible to write a regular expression that matches with digits that does not have integer on left or right side? If we have these strings:</p>
  
  <pre><code>a20c
   20c
  .20c
  a20-
  120
  </code></pre>
  
  <p>It should match the four first, but not the last one. </p>