title: Regex for NANP phone number with non-repeating last 7 digits
body: <p>I have to validate a 10 digit (US) phone number in the NANP format (no special characters allowed) in .NET and also check to make sure the last 7 digits of the phone number are non-repeating. So far, I have written the following regex to validate the NANP format</p>
  
  <pre><code>^(?:[2-9][0-8][0-9])([2-9][0-9]{2}[0-9]{4})$
  </code></pre>
  
  <p>How do I modify this regex to also account for non-repeating last 7 digits? Please note that using two regexes is not an option due to constraints of existing code.</p>
  
  <p>Edit:
  I have to check for consecutive duplicates in all 7 digits. For e.g. 2062222222 should be considered invalid whereas 2062221234 or 2062117777 should be considered valid.</p>
  
  <p>Thanks</p>