e.g. www.file.com/1000-2000/1211.txt

I want to check and see how many files there are on a site from the range from
say 1000-2000, since 3 out of 4 of the numbers I would put in come up 404
error.

Aka, I want an easy way to download all the files from a certain site without
having to manually put in 1000 numbers in hope that the ones I put in are
files, and avoid the ones that are 404 error.

Make sense? How can I do this?