Generate distinct random number using recursion in php

function generateRandomNumber($howmanynumber)
{
for($i=0; $i<$howmanynumber;$i++)
{
$random = mt_rand(1,53);
if($i == 0)
{
$rnum = $random;
}
elseif($i < 6)
{
$rnum = $rnum.",".$random;
}
else
{
$rnum = $random;
}
}
$rannum_arr = explode(",",$rnum);
$countnum = count(array_unique($rannum_arr));
if($countnum == 6)
{
return $rnum;
}
else
{
return generateRandomNumber(6);
}
}
$rannum = generateRandomNumber(6);
?>