That's a shame. I wonder if they're just hosting it on bad (wrong kind of cheap) servers or a bad company.
I don't know if the question in the title was serious but I came here to answer it very briefly anyway.
The codes are organized in groups. So there's not 513. There probably are 500-513, though. That group would have started with 500. Like a 404 error, which is within the 400 grouping. I can't recall what the term for these groupings is and I don't want to look it up.
There, now you have some of my incomplete, half-remembered and mostly useless knowledge.