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Old 2009-08-04, 22:51   #628
lycorn's Avatar
Sep 2002
Oeiras, Portugal

1,399 Posts

pi_rho is the forum nickname for Michael Schafer, of Michigan State University. His computer discovered the 40th known mersenne prime on the 17th of November 2003.
(and only now are we getting close to proving it is indeed M40!...)
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Old 2009-08-04, 22:55   #629
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"Tim Sorbera"
Aug 2006
San Antonio, TX USA

17·251 Posts

Originally Posted by Dougal View Post
Who is pi_rho,and what prime did he dicover?i cant the results of the prime he found,but it says he found one!
I got excited, but then I found he was the discoverer of M20996011 (which might be M40). Apparently all past primes were entered into the v5 system as successes (e.g. curtisc has two successes).

Last fiddled with by Mini-Geek on 2009-08-04 at 22:56
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Old 2009-10-07, 03:56   #630
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May 2005

BA16 Posts

Originally Posted by Primeinator View Post
Ah, okay. It did not look like there was an error code with the LL, though. Perhaps some other bug in the Prime95 caused it to beep? Perhaps it was something else on the computer? It would not beep prior to a test being completed...
It seems there Was an error on that LL. Someone has double-checked and triple-checked it now:

Verified test results
Exponent	User name	Computer name	Residue	Date found
28222361	ScottBardwick	SDB-Tosh-Lappy	82EA4572240B785E	2009-08-22 19:07
28222361	ScottBardwick	Q6600	82EA4572240B785E	2009-09-08 09:05


Bad test results
Exponent	User name	Computer name	Residue	Error code	Date found
28222361	S349120	CF9A4026F	1B7A5F9E15E942E4	00000000
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Old 2010-05-25, 18:43   #631
davieddy's Avatar
Dec 2006

2×3×13×83 Posts
Default Wagstaff refined

Originally Posted by CRGreathouse View Post
Doing the calculation slightly differently (prime-by-prime, splitting by value mod 4) I get an average of 2.411 Mersenne primes in that range.
(20M - 48M)
Originally Posted by R. Gerbicz View Post
I think it is better to do simulation, using conjecture for the probability that Mp is prime. 2000 simulations for the [2,5*10^7] interval, gives:
I've also counted the number of Mersenne primes in the runs. Note that using the conjecture the expected number of primes is about 48.9 (I've included p=2 in every cases).
Originally Posted by davieddy View Post
Glad (as always) to provoke mirth

But unless Gauss' 1/log k law is better expressed as
(1 + (log2 + log6)/(2log k))/log k, then the numbers bandied about
(1.78 mersenne primes between exponents x and 2x, gradient of
the log exponent graph etc) are out by about 10% for the
range tested to date.
I thought this was worth pointing out.


I have been bothered for a long time about neglecting
log a (a=2 or 6) in the formula for the probability of
a random exponent yielding a Mersenne Prime.
Both Greathouse and Gerbicz used the third part of
the conjecture on each prime exponent, and their results
confirm my suspicion. Furthermore, the approximation is

(egamma/log2)(1/k + (log2+log6)/2/klogk)

Integrate to get the expected number of Mersennes up to k:

(egamma/log2)(logk + log(logk)(log2+log6)/2)

Between 20M and 48M we expect:

log(48/20)/log1.47576 + 1.242log(log48M/log20M)/log1.47576

= 2.2496 + 0.1621
= 2.4117

The second term adds 7.2% -- hardly neglible!

The small k to k=50M case is more problematic, but note that
log(50M/2)/log1.47576 is only 43.7


Last fiddled with by davieddy on 2010-05-25 at 19:14
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Old 2010-05-26, 10:33   #632
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Dec 2006

2×3×13×83 Posts

The expected number of Mersenne primes with exponents
between x and x^2 is:

(logx/log1.47576) + 2.2129

So between 7000 and 49000000 we expect

22.75 + 2.2129
Or 25 +/- 5

between 83 and 7000 we expect
11.375 + 2.2129
between 9 and 83 we expect
5.69 + 2.2129


Last fiddled with by davieddy on 2010-05-26 at 11:18
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