Generate a registrant number on pre-defined range

Hi,

I will need your help to create a code to generate a registrant number on a pre-defined range.

For example , on some event the range will be between 1000 and 2000,

and a number will be automatically generated when the users makes his registration on that event (1150 for example)

This number will also appear on the event registration list.

Thanks in advance.

Joaquim