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Old 2003-05-27, 21:50   #1
May 2003

210 Posts
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Hi, I'm kind of ignorant in terms of this math, and if someone had some spare time, could they explain it, b/c I couldn't understand the site when it tried to explain it. Such as, what does m128493 mean? (I just made up the numbers with m in front.) Thank you.
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Old 2003-05-27, 21:52   #2
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Aug 2002

2·101 Posts

It means 2^128493-1. As a number expressed in binary, it has 128,493 1's.
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Old 2003-05-28, 00:44   #3
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"Richard B. Woods"
Aug 2002
Wisconsin USA

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In our branch of math, the M in M128493 is in honor of Marin Mersenne, a French monk who first popularized the study of this category of numbers. (He also did a lot more for math, but these "Mersenne numbers" are probably his most famous legacy.)

One of the neat things about math is that if you discover something new that becomes popular with other mathematicians, they often name it after you. One mathematician I knew a while ago, Robert Thomason, discovered several new things in a field called algebraic topology, so now has some theorems and other math stuff named for him.

I don't know if you're familiar with the notation 2^128493-1. For the sake of anyone reading this who isn't familiar with that -- let's put it this way: 2^3 means 2 x 2 x 2, which equals 8. Note that the "3" on the right-hand side of the "^" in "2^3" is the number of 2's that are multiplied together. 2^5 means 2 x 2 x 2 x 2 x 2. 2^128493 means 2 x 2 x 2 x 2 x 2 x 2 x ... (on and on to the 128493rd "2") = 128493 twos multipled together. 2^128493-1 just means to multiply 128493 twos together then subtract 1 from that result.
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