$(document).ready(function() {
  $('#number-btn').mousedown(redirect);
});

function redirect() {
  var btn = $('#number-btn');
  var val = $('#number').val();
  if (val < 0) {
    val = 0;
  }
  $(btn).attr('href', $(btn).attr('url') + 'number/' + val + '.html?height=100&width=300');
}