Wordpress/show certain category IDs in a main menu?

I've been away from Wordpress for so long that I've forgotten how to do this. I want items to appear in my main menu, only if they are of certain category IDs. For instance, this is the code pulling in links on my main menu:

<div id="subnavbar">
	<ul id="subnav">
		<?php wp_list_categories('sort_column=name&title_li=&depth=3'); ?>
	</ul>
</div>

Code (markup):

how do I make it so that only category ID #21 and category ID #40 will show up in the menu?

EDIT: nevermind, figured it out. Here's the answer to this:

<div id="subnavbar">
	<ul id="subnav">
	<?php wp_list_categories('sort_column=name&include=21,40&title_li=&depth=3'); ?> 
	</ul>
</div>

Code (markup):