title: Regex for the number that should not start with some specific two digit numbers
body: <p>I am trying to build a regex for following rules</p>
  <ol>
  <li>No characters – only numbers are allowed to enter</li>
  <li>Numbers must contain not less than 8 digits</li>
  <li>Numbers and combinations, starting as follows should not be allowed:
  <ul>
  <li>[3.1]  - Any number starting with 0 (zero) and with 1 (one);</li>
  <li>[3.2] - Numbers starting with 20, 21, 22, 23, 24, 25, 26, and 27.</li>
  </ul>
  </li>
  </ol>
  <p>I am able to achieve regex for points <code>1</code>, <code>2</code> and <code>3.1</code> like this</p>
  <pre><code>^[2-9]{1}[0-9]{7,}$
  </code></pre>
  <p>But I am not able to find solution for point <code>3.2</code></p>
  <p>This is one of the options I started with, this regex matches the string that must start with 20, 21, 22, 23, 24, 25, 26, or 27.</p>
  <pre><code>^([2][0-7])[2-9]{1}[0-9]{7,}$
  </code></pre>
  <p>I just have to find the negation of this first condition.</p>
  <p>Please help!</p>