obscur.com.php

<?php
$j=$a=1;
echo '<ul>';
do{
  $a = $a << 1;
  $i = ($a-$j)%2;
  $class = empty($i)?'e':'o';
  echo '<li class="'.$class.'">'.$j.'</li>';
  $j++;
} while($j<=10);
echo '</ul>';