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2020-01-24, 01:08   #9
storm5510
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Aug 2009
U.S.A.

133810 Posts

Quote:
 Originally Posted by Dr Sardonicus The number of decimal digits in 10*2^13509-1 would also be 2 + floor(13509*log(2)/log(10))...
I am going to spread this out a bit so I can read it better with my bad eyes. Sorry!

2 + floor(13509 * log(2) / log(10))

I carefully worked this through Windows Calculator and came up with 25,151. I am not sure about "floor" but it is familiar. So, I tried the same formula on this:

Code:
231*2^2335281-1 is prime! 702992 digits.
4,544,874. So I must not be doing something properly.