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Thread: identify

  1. #1 identify 
    Forum Sophomore
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    is there any way one can identify a prime number just looking at the digits?


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  3. #2  
    Forum Ph.D.
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    No.

    But you can sometimes tell if a number is not a prime Ė e.g. itís even and greater than 2, or the sum of its digits is divisible by 3 (and itís not 3 itself), or the last digit is 5 (and itís not 5 itself), etc.


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  4. #3  
    Forum Professor river_rat's Avatar
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    Well you can always show that is divisible by

    more seriously, look into the famous AKS algorithm.
    As is often the case with technical subjects we are presented with an unfortunate choice: an explanation that is accurate but incomprehensible, or comprehensible but wrong.
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  5. #4  
    Forum Masters Degree thyristor's Avatar
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    Isn't it called Wilson's theorem? However it's not very useful for very large numbers. Think of 100000!...
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  6. #5  
    Forum Masters Degree thyristor's Avatar
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    What you really need, is to be able to to factorize any number, and to be able to do it fast.
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  7. #6  
    . DrRocket's Avatar
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    Quote Originally Posted by thyristor
    What you really need, is to be able to to factorize any number, and to be able to do it fast.
    I don't know about "need", but if you can do that you will have trashed some of the world's most secure current codes. And that is why there is so much work going on to figure out how one might do it.
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  8. #7  
    Forum Masters Degree thyristor's Avatar
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    I mean that if you can factorize any number fast, you can also see if it is a prime or not since if it is a prime it has only got itself and one as prime factors.
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