<?php
$aantal = 10;
for($x = 1; $x <=10; $x++) {
 echo $x.str_repeat("_", $x).$x."\n\r";
}
?> 

1_1

2__2

3___3

4____4

5_____5

6______6

7_______7

8________8

9_________9

10__________10