I need a random number within a range, and not to duplicate the numbers in current list

Hi all! Here is what I am doing. Our students have a alternate student number which is what they use for email, computer login, etc... the syntax is the first four numbers are 1010 and the last four are the variable...for example 10102342 is one student and 10102393 could be a another student. The range is 10100001-10109999. I currently have just under 1000 students with 1010#'s already, so I would like to create a button on a form that would generate a 1010xxxx number without duplicating the current numbers.

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Thanks in advance!!

My form has a text box (txtGenerate) which is the output; where the 1010# should show up. A command button (cmdGenerate) which is where the user will interact and click the button to generate the 1010#..