Files with purely numerical names like this often appear in:

If you have 7-Zip installed, run 7z l 3187800576.7z in your terminal to list all contained files, their sizes, and original timestamps.

To see what is inside this specific file without fully extracting it, you can use several methods:

Applications like File Roller or Archiver can open .7z files to display a visual file list. Common Sources for Such Files

Platforms like the Internet Archive often use numerical identifiers for their catalog items. Archiver: Easier Way To Extract Archives