How 'Hell Levels' work.

[maestrom]

I've done a little bit of digging and I haven't been able to find any information on why leveling worked the way it did in classic.

I remember hearing at one point that Hell Levels were an unintended result of how experience needed to level was calculated using their formula. I've been thinking about this for a long time and I can't figure out a formula that would behave this way unless you were specifically intending to make every 5th level past 25 take a ton more experience.

Does anyone know the backstory to hell levels or actually have the original formulas they used?