Since this is an older version, it is no longer featured on the primary Oracle SQL Developer Downloads page. You can typically find it through the following official channels:
Suppose you are a database administrator tasked with creating a new table in an Oracle database. Using Oracle SQL Developer 3.2.20.10, you can: Oracle Sql Developer 3.2.20.10 Download
This was the first version to officially support the 12c database. Since this is an older version, it is
Before installing Oracle SQL Developer 3.2.20.10, ensure that your system meets the minimum requirements: Since this is an older version
If you have an active support contract, you can search for and download legacy patch sets directly from My Oracle Support Oracle Full Client Bundles:
Where can I find old versions of SQL Developer (4.x)? [closed]