- var_dump: documentation ( source)
- array_reverse: documentation ( source)
- preg_match_all: documentation ( source)
- strtoupper: documentation ( source)
- dechex: documentation ( source)
- str_pad: documentation ( source)
<?php
$number = 1234567890;
$hex = strtoupper(dechex($number));
$hex_padded = str_pad($hex, 9*2, "0", STR_PAD_LEFT);
preg_match_all('/.{2}/', $hex_padded, $matches);
$result = array_reverse($matches[0]);
var_dump($result);