It is mandatory to provide the AO Code while applying for PAN and TAN. AO Code (i.e., Area Code, AO Type, Range Code and AO Number) of the Jurisdictional Assessing Officer must be filled up by the applicant. These details can be obtained from following links  :

https://tin.tin.proteantech.in/pan/servlet/AOSearch

Click on above link  for AO Code of PAN.

https://tin.tin.proteantech.in/tan/servlet/TanAOSearch

Click on above link  for AO Code of TAN.