title: Removing whitespace between consecutive numbers
body: <p>I have a string, from which I want to remove the whitespaces <em>between the numbers</em>:</p>
  
  <pre><code>string test = "Some Words 1 2 3 4";
  string result = Regex.Replace(test, @"(\d)\s(\d)", @"$1$2");
  </code></pre>
  
  <p>the expected/desired result would be:</p>
  
  <pre><code>"Some Words 1234"
  </code></pre>
  
  <p>but I retrieve the following:</p>
  
  <pre><code>"Some Words 12 34"
  </code></pre>
  
  <p>What am I doing wrong here?</p>
  
  <p>Further examples:</p>
  
  <pre><code>Input:  "Some Words That Should not be replaced 12 9 123 4 12"
  Output: "Some Words That Should not be replaced 129123412"
  
  Input:  "test 9 8"
  Output: "test 98"
  
  Input:  "t e s t 9 8"
  Output: "t e s t 98"
  
  Input:  "Another 12 000"
  Output: "Another 12000"
  </code></pre>