How to generate random number in wordpress?

I want to generate random number from word press admin panel,like when i click on posts ,where i enter the number let suppose i enter the 100,then 100 random number will be generated,after that in next tab i can add the some fields and assign a random number to the adding fields...please guide me any type of plugin or code i am newbie to php ,any php expert can my help.

function binary_book() {

register_post_type( 'book', array(
  'labels' => array(
    'name' => 'Books',
    'singular_name' => 'Book',
   ),
  'description' => 'Books which we will be discussing on this blog.',
  'public' => true,
  'menu_position' => 20,
  'supports' => array( 'title', 'custom-fields' )
));
}