Combine next or number for WordPress wp_link_pages <!--nextpage--> function.

content.php

<?php wp_link_pages(array( 'before' => '<div class="page-links"><span class="page-links-title">' . __( 'Pages:', 'twentythirteen' ) . '</span>', 'after' => '</div>', 'link_before' => '<span>', 'link_after' => '</span>', 'next_or_number' => 'next_and_number', 'separator' => '', 'nextpagelink' => __( '&raquo;' ), 'previouspagelink' => __( '&laquo;' ), 'pagelink' => '%')); ?>

functions.php

<?php

/**
 * Filter wp_link_pages to do both next and number
 */
 
add_filter('wp_link_pages_args', 'wp_link_pages_args_prevnext_add');
/**
 * Add prev and next links to a numbered link list
 */
function wp_link_pages_args_prevnext_add($args)
{
    global $page, $numpages, $more, $pagenow;

    if (!$args['next_or_number'] == 'next_and_number') 
        return $args; # exit early

    $args['next_or_number'] = 'number'; # keep numbering for the main part
    if (!$more)
        return $args; # exit early

    if($page-1) # there is a previous page
        $args['before'] .= _wp_link_page($page-1)
            . $args['link_before']. $args['previouspagelink'] . $args['link_after'] . '</a>'
        ;

    if ($page<$numpages) # there is a next page
        $args['after'] = _wp_link_page($page+1)
            . $args['link_before'] . $args['nextpagelink'] . $args['link_after'] . '</a>'
            . $args['after']
        ;

    return $args;
}