.thumbdata3--number is Android MediaProvider thumbnail database
Key Features: .THUMBDATA3--NUMBER File Extension
|Created by||Google Inc.|
What is an .THUMBDATA3--NUMBER file?
The thumbdata3--[various numbers] file extension is associated with Google Android OS.
The thumbdata3 files contain generated thumbnail database of pictures, found in DCIM folder mostly on SD card of Android phone. These files can be pretty large, but if you need you can freely delete them. If needed the app will recreate them again.
The numbers behind the file extension are probably generated randomly depending on the device or something else.
Example of these files includes: