How to add a auto-increment reference number field to custom object

Summary:

I have a Custom Object, The primary key is the id, however i would like to add a reference number field like one we get when creating INCIDENTS

Content (required):

The standard object incident has a reference number field, which is automatically incremented and updated for every incident that is generated (through rest api and agent BUI).

I have a custom object but i am unable to mimic this functionality. Is this possible through business rules? If so, any documentation would be very helpful!

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