What is the next number 13211311123113112211 ?

Funny sequence

<?php
$sequence[0] = '1';

//$sequence[1] = (count of numbers in $sequence[0]) //11
//$sequence[2] = (count of numbers in $sequence[1]) //21

function populate_sequence_row($sequence, $rowNumber)
{
	if($rowNumber == 0) return 1;
	$order = array();
	$tmp = '';
	$output = '';
	$str2array = preg_split("//", $sequence[$rowNumber-1], -1, PREG_SPLIT_NO_EMPTY);
	foreach($str2array as $value) {
		$prev = count($order) - 1;
		if(isset($order[$prev]) && $tmp == $value) {
			$order[$prev]['count']++;
		} else {
			$order[] = array('number' => $value, 'count' => 1);
	   }
		$tmp = $value;
	}
	foreach($order as $key => $value) {
		$output .= $value['count'] . $value['number'];
	}
	return $output;
}

if(!isset($argv[1])) exit("Script use: php sequence.php <number>\n");

$n = $argv[1];

for($i = 1; $i<$n; $i++) {
	$sequence[$i] = populate_sequence_row($sequence, $i);
}

var_dump($sequence);