If all you want is just to generate random numbers, you must know the max and the min. So therefore you could use the very simple PHP function: mt_rand(); or simply rand() which doesn't need to seed the random generated number as of php 4.4.x
Refresh that and you'll get several random generated numbers between those two min and max.
//Generating Random Numbers From 11111111 to 99999999
$min=11111111; //Number MUST be integer so we don't quote it
However, the issue that comes into play here is the one about the random numbers repeating themselves after a certain period of time. I could do a small script that'll keep the generated numbers in mind into a mysql table or a plain file. That'll not come for free though BUT heck I think you got the idea and I'm sure you can do it now.