Try this
PHP Code:
<?php
$url = '/category/3/pictures45.html';
preg_match('/\/category\/([0-9]+)\/([a-z]+)([0-9]+)/i', $url, $match);
echo('<pre>' . print_r($match, true) . '</pre>');
$id = $match[1];
$pagenumber = $match[3];
echo ('<p> ID = ' . $id . '</p>');
echo ('<p> Page number = ' . $pagenumber . '</p>');
?>