How Do I populate a table with seqential numbers

[Red Eye]

I have a table of information. I want to generate a unique id on a certain given formula. The first 3 letters of the id are generated via a formula depending upon company name, location etc. the next 3 digits are sequential. I want the user to be able to input the first 3 digits, input the amount of id's i.e. 200 then hit a button to create them and the rest of the fields. What is the best way of doing this?