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Automating Reduction by a Varying Modulus 
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#1
Mar113, 11:09 PM

P: 74

Hey guys,
I'm doing some experimenting recently with some primality tests, and I need help figuring out how to automate the following: Given an even number N, divide by 2k ([itex]k \in \mathbb{N}[/itex]). If N/2k is an integer, reduce mod 2k+1. (If N/2k is not an integer, simply move on to the next one.) Do this for all 2k ≤ N/2. Then print those k (or 2k, doesn't really matter to me) for which the resulting reduction by the modulus 2k+1 is odd. EX: N = 20. 20/2 [itex]\equiv[/itex] 1 (mod 3). 20/4 [itex]\equiv[/itex] 0 (mod 5). 20/6 noninteger. 20/8 noninteger. 20/10 [itex]\equiv[/itex] 10 (mod 11). Print: 2k = 2 (or k = 1), since this is the only odd reduction that was obtained. If it helps, I have Mathematica and Maple, as well as some basic understanding of LaTeX, but my programming skills are pretty crappy. Thanks in advance! P. S. I wasn't sure if I should post this in the Computer Science forum, but I figured that it's more of a math topic anyway, and there are bound to be some math people who know how to do this. 


#2
Mar213, 12:13 AM

Mentor
P: 21,313




#3
Mar213, 08:29 AM

P: 74

Oops my bad. That should have been a 2, yeah. The Sieve of Eratosthenes is not what I'm looking for though. I'm not expecting anyone to see my logic in doing this, just wondering if anyone knows how.



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