<?php
$num = 10;
$sequence = [
1,
2,2,
3,3,3,
4,4,4,4,
5,5,5,5,5,
6,6,6,6,6,6,
7,7,7,7,7,7,7,
8,8,8,8,8,8,8,8,
9,9,9,9,9,9,9,9,9
];
function reverse ($sequence,$num){
$num--;
if ($num>=0){
echo $sequence[$num];
reverse($sequence,$num);
}
}
reverse ($sequence,$num);