Now that I am doing a lot of P-1 I'm intrigued by the number of relative primes

Code:

[Nov 5 17:57] Available memory is 3151MB.
[Nov 5 17:57] Using 3141MB of memory. Processing 144 relative primes (259 of 960 already processed).

All my recent P-1 work has been for exponents in the 40-59M ranges; yet I see "relative primes" ranging from 144 to 960 with many values between.

At one time I thought it might be some magical function of the exponent range...until yesterday.

I have a PC working on P-1 in the 47.2M range and for 5 days it was doing 480 relative primes; which by the way is the most common value I've seem for P-1.

However, last night I changed the CPU setting to increase RAM overnight (it is now 16G daytime and 20G overnight). Since then the P-1 work on this same PC is now doing 960 rp's.

Now I am thinking the value is a function of the RAM allocated.

I am going to further assume it is a function of the maximum RAM; otherwise assignments starting during the day (when I have 16G) would get 480 rp's and 960 rp's when started overnight.

Am I anywhere close is my guesses?

Is there a layman's answer to this question?