Quote:
Originally Posted by odin
It takes about 18 hours to Trial factor one increment like from 2^68 to 2^69 so 36 hours to go from 2^68 to 2^70

If it takes you 18 hours to do 68 > 69, then it will take you 36 hours to do 69 > 70, for a total of 54 hours.
Each bit increase represents a DOUBLING of the work done in the previous level.
To put it another way, it would take the same amount of CPU time to trial factor from scratch to 69, as it would to trial factor from 69 to 70.