- substr: documentation ( source)
- str_pad: documentation ( source)
<?php
$c5 = 215601;
$c1 = 6;
$p = str_pad($c1, 3, '0', STR_PAD_LEFT) . str_pad($c5, 10, '0', STR_PAD_LEFT);
$ctr = 22;
$ctro = '0' . substr($p,2,2) . substr($p,7);
echo $p;
echo '-';
echo $ctro;