I think you guys went about calculating that number wrong.

(even though Moore's law is only the doubling of transistors, not performance)
The performance should supposedly double every 18 months if the doubling of transistors meant doubling the performance, so
One Sandy Bridge processor*2^(years/1.5)-I'm only going to go 30 years.
50,000*2^20=52,488,000-This is the PPD one processor would get 30 years from now.
Now divide that number bean threw out by the PPD
20,000,000,000,000,000/52,488,000=~381029475-This is the days it would take to complete that number.
Now make that into years
381029475/365=113,236 years
For 1 processor to make that number in 30 years, that would take it 113,236 more years to get there, but there are going to be more than 200,000 processors folding most likely, so the folding project could get there lightning fast.
113,236/200,000= ~1/2 a year
You forgot that when you have the number to a power, you're more than doubling the amount of PPD per 18 months that F@H would supposedly get.
😉
I don't want to bother trying to calculate the PPD of f@h at that time, because that would mean you have to know what older computers would supposedly be folding still. Just leave it as a simple calculation like this.