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:
Click on below link for AO Code of PAN:
https://tin.tin.nsdl.com/pan/servlet/AOSearch
Click on below link for AO Code of TAN:
https://tin.tin.nsdl.com/tan/servlet/TanAOSearch
Source: Income Tax India’s Official Website