Where you found this string is the biggest clue to its identity:
Often, specific numbers become "codes" for certain types of internet content: 20613mp4
Occasionally, numbers refer to "found footage" or lost media projects (like the Backrooms or SCP Foundation series). Where you found this string is the biggest
If the file is safe but won't play, you can use to look at the metadata. This will tell you: The encoding date (when the video was made). 20613mp4
The (if it was recorded on a phone and metadata wasn't stripped).