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Old 2020-01-24, 14:50   #16
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storm5510's Avatar
Aug 2009

32·137 Posts

Originally Posted by LaurV View Post
...Your confusion may be because log in your case is assumed to be any base (like natural log). If you take base 10, log10(10) is 1, so the last part is gone. Note that in windows calculator, log is base 10 (what we use in school to write like lg) and not base e (what we used in school to write like ln).
I think you are probably correct. Perhaps Windows calculator is not doing this correctly. It has "log" and "ln." I have always taken the first to mean base 10, and the second, base 2. Either way, I cannot get it to come up with a correct value based on what I have seen here.

Originally Posted by kar_bon
You should also use the normalized form instead:
10*2^n-1 = 5*2^(n+1)-1, see here for those primes.
I looked. All of this seems to be locked in on 5, or perhaps, multiples of 5.

Originally Posted by Dr Sardonicus
Siccing the mighty Pari-GP on the previous query,
This must be an expression calculator. I found a few online but none could return a value of any size.

I looked at some of the prime results posted above. I noticed some of them use composite numbers, like 231*2^2335281-1. At first, I thought this would be self-defeating, but then, I remembered some basics: Odd number * odd number is an odd number. Just in case, I steered around this. Below is a PFGW ABC2 I had been experimenting with.

ABC2 $a*2^$b-1
a: primes from 100 to 500
b: from 4256191 to 4256191
The "b" number is a natural from a long list I created with a simple Perl script. Repeating it was the only way I could find to keep it static while being able to increment the "a." I was amazed at the different operator combinations I could use.

I want to thank all of you for your feedback so far. Most kind.

Last fiddled with by storm5510 on 2020-01-24 at 14:51 Reason: Typo
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