How can I get a table with the number of published posts by date?

by

the fastest way imho would be to create a custom sql statement:

global $wpdb;
$rows = $wpdb->query('SELECT DATE(post_date) AS date, COUNT(*) AS count FROM ' . $wpdb->posts . ' GROUP BY DATE(post_date) ORDER BY DATE(post_date)');
foreach ($rows as $row) {
    echo $row->date . ': ' . $row->count . '<br>';
}