title: Need a regex for a string that must have letters but can't have purely numbers and cant have special chars
body: <p>Need a regex for string such that:</p>
  
  <ol>
  <li>Can have letters, numbers</li>
  <li>ignore special characters like: &lt; > { } [ ] # ~ ^/\"</li>
  <li>Can't have purely numbers</li>
  <li>Max size is 20 chars</li>
  </ol>
  
  <p>Valid answers
  a) "hello world 123 -"
  b) "123 hello - world"
  c) "- hello 123 world"</p>
  
  <p>Invalid answers
  a) "123456"
  b) "123456 "
  c) "abc>>>"
  c) "abc123>>>"
  d) ">>>>"
  The closest i've come up with is:</p>
  
  <pre><code>^([A-Za-z0-9 '\-!\£\$:;%&amp;amp;\*\(\)_=\+,.\?@\n\r\t]{1,20}$
  </code></pre>
  
  <p>But point 3 of "Can't have purely numbers" becomes invalid.</p>
  
  <p>Any idea?</p>