In this business scenario the requirement is to generate an Auto-Number on the Account entity. The specific requirement is that the first 3 characters of the account name is used as a prefix and that when generating the AutoNumber we need to count the number of existing prefix records & increment by one.
As always whenever we are using the North52 Auto-Number formula type we are guaranteed consistency when generating Auto-Numbers so no duplicates will be created even with multiple application servers for any of CRM Online, OnPremise or Partner Hosted.
It is assumed that the 'Account Number' field is read-only, accounts are never deleted (only deactivated) & users cannot change the field.