Magento how to get category id in product page?

<?php $categories = $_product->getCategoryIds(); ?>
<?php foreach($categories as $k => $_category_id): ?>
    <?php $_category = Mage::getModel('catalog/category')->load($_category_id) ?>
    <a href="<?php echo $_category->getUrl() ?>"><?php echo $_category->getName() ?></a>
<?php endforeach; ?> 

This will load and link all of the categories that the product is found in.