Sequential Numbering in a Column

Sequential Numbering in a Column

Use Case: I'm using Zoho Reports to compile the results of an online exam and issue certificates based on the exam completion.  I would like to number these sequentially as they come into Zoho Reports via an API.  So starting with, say, certificate 1507, the next entry into the database should be 1507+1=1508.  Is there a way to apply a formula to a Certificate # column so that incoming data is assigned a unique, sequential number?  

Any help would be much appreciated!