Look I have something more elaborated that doesn't work. I hope it helps you understand what i'm trying to get:
// $numbers = '';
// for($i=0;$i<=9;$i++){
// $rannumberi= '';
// $rannumber.= mt_rand(1, 10);
// // if(strstr($numbers, $rannumber) == FALSE) {
// print($numbers).'<br>';
// $numbers.= $rannumber;
// // }else{
// // $i = $i - 1;
// // }
// }