20210517, 23:30  #1 
"David Kirkby"
Jan 2021
Althorne, Essex, UK
11×37 Posts 
Is there an accepted standard for refering to Mersenne Prime numbers?
I'm a bit confused by what seems to be an inconsistent way of numbering Mersenne prime numbers. For example, is the 19th Mersenne prime (2^89 1 = 618970019642690137449562111)
M10  since it is the 10th one. M(10)  since it is the 10th one. M(89)  since the exponent is 89 M89  since the exponent is 89 M6,189,70,019,642,690,137,449,562,111 M(6,189,70,019,642,690,137,449,562,111) something else? And how about Mersenne numbers which are not prime  eg 2^11 1 = 2047 = 23*89 ? Last fiddled with by drkirkby on 20210517 at 23:31 
20210517, 23:38  #2  
If I May
"Chris Halsall"
Sep 2002
Barbados
2^{3}·23·53 Posts 
Quote:
You seem to be a fairly smart person. You give enough information for us to be able to drill down and find you have a PhD. And yet you seem to ask some very stupid questions. The question is... why do you do this? 

20210518, 00:42  #3  
"David Kirkby"
Jan 2021
Althorne, Essex, UK
110010111_{2} Posts 
Quote:
I don't think the question is so stupid, as the literature is inconsistent on this. The terms don't seem to be used consistently on these forums Here https://www.mersenneforum.org/showthread.php?t=23892 Uncwilly asks people to predict M52. yet here, https://www.mersenne.ca/exponent/103750501 in the top left, we see M103750501, and read further down "No known factors for M103,750,501" So there are two conflicting examples of representing the numbers. I have seen others too. In cases the context makes it fairly obvious, but M17 could refer to 2^17 1 or the 17th Mersenne Prime which is 2^2381 1. Here, parentheses are used. https://www.math.wichita.edu/history/men/mersenne.html it says "Currently GIMPS is checking and double checking to verify (prove) that M(6972593) is indeed the 38th Mersenne Prime." So that's 3 different ways. Perhaps I just have to accept the inconsistency, but I would not expect that from mathematicians. Dave Last fiddled with by drkirkby on 20210518 at 00:44 

20210518, 01:04  #4  
6809 > 6502
"""""""""""""""""""
Aug 2003
101×103 Posts
3^{4}·11^{2} Posts 
Quote:
Also, a rule of thumb is to check the wiki to find answers for questions like this. Also, there is not a big need for excessive blank lines in posts. 

20210518, 01:08  #5  
Feb 2017
Nowhere
5×7^{2}×19 Posts 
Quote:
A similar situation exists with "repunit" numbers (10^{k}  1)/9. R_{n} can mean the n^{th} repunit prime (or probable prime), as in a graph posted to a recent thread. But in a statement like "R_{8177207} is a PRP" the subscript clearly means the exponent. 

20210518, 02:25  #6 
"TF79LL86GIMPS96gpu17"
Mar 2017
US midwest
11·491 Posts 
There's a simple way to avoid or reduce the ambiguity. See https://www.mersenneforum.org/showpo...67&postcount=4

20210518, 07:37  #7  
"David Kirkby"
Jan 2021
Althorne, Essex, UK
11×37 Posts 
Quote:
I think the comment from chalsall that this was a very stupid question is a little unfair, but he/she is entitled to their opinion. As to the spaces, whenever I write a post on here, extra spaces get added. Unusually I remove them in the preview, or immediately go back and edit the post. I get the same problem whether I use Firefox on Windoze, Linux or Solaris. I must have omitted to do both in this case. Dave 

20210518, 07:56  #8  
"TF79LL86GIMPS96gpu17"
Mar 2017
US midwest
1010100011001_{2} Posts 
Quote:
For more clarity, we would use Mx for 2^{x}1, Mpy=yth Mersenne prime, or Mpy=Mx. But due to past practice, using Mx for both xth and 2^{x}1, Mx is inconveniently ambiguous for x<~53 at the moment, x prime, 2^{x}1 prime; 2 3 5 7 13 17 19 31, 8 cases. Writing "Mp2=M(3)" where M(x) = f(x) =2^{x}1 could help. Or perhaps Mp#2 = M3 = 7; Mn11=2047. Mp#x concisely abbreviates "Mersenne prime number" x, signifying position in the list of known Mersenne primes. The usual convention is to follow with an asterisk, those that are not verified up to, as Mp48*  Mp51*. https://www.mersenne.org/primes/ There's value to readers in writing clearly enough once, that numerous readers needn't think much to disambiguate what's written, every time it's read, and not assuming or requiring as much prior knowledge. We do occasionally get total noobs here on the forum, who've just learned of Mersenne numbers, and are reading here out of curiosity. The extralinebreaks phenomenon/nuisance began sometime after 2016. It did not occur when I first joined in early 2017. A habit to use Advanced Edit, and Preview Changes always, helps. It appears to be a Firefox related issue; MS Edge does not have it, based on a very brief test. OEIS has https://oeis.org/A000668 (Mersenne primes) and https://oeis.org/A000043 (exponents of Mersenne primes) Last fiddled with by kriesel on 20210518 at 08:57 

20210518, 10:56  #9  
Apr 2020
16D_{16} Posts 
Quote:
Last fiddled with by charybdis on 20210518 at 10:57 

20210518, 12:29  #10 
Einyen
Dec 2003
Denmark
7×11×41 Posts 
Other options could be: M#52 or M52# or M52nd/M47th etc.

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