This is usually a database index or a timestamp . In many automated scraping or archiving systems, files are assigned numerical IDs to keep them organized.
In the modern day, names like this are often viewed with . They represent a "Wild West" era of the internet before sophisticated algorithms and SEO-optimized titles took over. Today, you are more likely to encounter such a name in: Old hard drives or "digital time capsules." Sexy Girl (2561) mp4
A file named like this typically comes from one of three places: This is usually a database index or a timestamp