$re = '/(\d+)\s\(\s(\d+)\s\)|(\d+)(?=\s\(\s(?:\d+\s\(\s\d+\s\)\s)+(\d+))/';
$str = '3 ( 16 ) 23 ( 24 ( 40 ) 50 ( 66 ) 76 ) 83 ( 88 ( 104 ) 127 )';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php