I wanted to show post from just recent post from a specific categories

so far this is what I have but:

<ul>
    <?php
    $number_recents_post = 5;
      $recent_posts = wp_get_recent_posts($number_recents_post);
      foreach($recent_posts as $post){
        echo '<li><a href="' . get_permalink($post["ID"]) . '" title="Look '.$post["post_title"].'" >' .   $post["post_title"].'</a> </li> ';
      } ?>
    </ul>

I tried turning it into this but not working

<ul>
    <?php
    $number_recents_post = 5;
      $recent_posts = wp_get_recent_posts($number_recents_post . 'cat=3,4,5');
      foreach($recent_posts as $post){
        echo '<li><a href="' . get_permalink($post["ID"]) . '" title="Look '.$post["post_title"].'" >' .   $post["post_title"].'</a> </li> ';
      } ?>
    </ul>

Please let me know what am I doing wrong....