I have an anchor like this:

<a href="#" rel="1 4 7 18 ">Anchor</a>

Where 'rel' attribute values are ids of some items.
Than I have a form with an input, where user should type an id and click submit button.
On submit button click I need to check the value of input like this:

var value = $('a').attr('rel');
if ( value == '1' || value == '4' || value == '7' || value == '18') {
// however I need the line above are created dynamically based on 'value' var
  alert('The id exists');
  return false;
} else {
  return true;
}

So, the question is how to create a line below dynamically based on anchor 'rel' attribute values?!
This is the line:

if ( value == '1' || value == '4' || value == '7' || value == '18') {