CRM 2016 : Number auto sequence with different prefix

Hi all,

I have one custom entity and on that entity I have one attribute called as Department.
I need to auto number the sequence of the department.
Department: 
Washington DC
New York
Chicago

If department = Washington DC then Serial number is WDC#101 for the record
If department = New York then Serial number is NY#201 for the record
If department = Chicago then Serial number is CHI#301 for the record

Every time if I create a record I need to show the respective department sequence number that should increase from with respective to their prefix number.

For this please let me know how to implement logic.

Thanks,