Over time I've developed a sense of the GPU factoring process, including an idea of the general proportion of TF exponents that come out as Not Prime and how long (in GHz-Days) it takes to factor to various exponent levels.

Thus, for example, I can grasp how "dbaugh," who stands at #5 on the

Top Trial Factoring Producers list, could have such a large number of GHz-Days for the small number of TF attempts: I attribute this to factoring to very deep levels. (Right?)

However, there is one remarkable phenomenon that leaves me scratching my head. How can #16, Bill Staffen, have found only 2 factors in more than eight thousand tries? Is it simply bad luck, or can someone explain (in not too-technical terms -- I'm no mathematician

) how that can be?

Typical success seems to run in the 1 - 1.5 percent range. How does one manage to get less than 0.025 percent? What exponent range and to what levels might one work on to achieve this?

Just curious...

Rodrigo