The lowest and highest md5 filenames on e621, found via order:md5_asc and order:md5, both begin with 5 repeating digits.
Which is what one would expect, as 16^5 is a bit over one million, and e621 has 2.5 million files.
But chances are good there's a filename beginning with 6 repeating digits besides 0 or F (111111, 222222, etc). Anyone know how to find them?

Has there ever been a MD5 collision on e6 yet?