Генерация промо-кодов

$db = new DB();

$num = [1,2,3,4,5,6,7,8,9];
$let = ['A','B','C','D','E','F','J','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'];

$arr = [];

for($i = 0; $i < count($num); $i++){
    for($j = 0; $j < count($num); $j++){
        for($k = 0; $k < count($let); $k++){

            $arr = "T{$num[$i]}{$num[$j]}{$let[$k]}";
            $db->query("INSERT INTO `promo_code` SET `code`='".$arr."', `target`='test', `days`='14' ");
        }
    }
}