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Prime factorization for large numbers

  1. Aug 22, 2011 #1
    I need to factorize large numbers (some of them have about 200 decimal digits). Wolfram alpha is a dead end and programming with python is not working for me too. Any suggestions?
     
  2. jcsd
  3. Aug 23, 2011 #2

    phyzguy

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  4. Aug 23, 2011 #3
    Oops. Sorry! I did miss a REALLY important thing(!!): they are really so simple/silly! They are full of zeros, for example one of them is 909091 with 150 zeros after it, so the only problem would be factorizing 909091 and that's not a big deal. so the answer of the given number will be 909091*2^150*5^150. There is a list of them (523 numbers) and they are between 100 and 200 digits and most of them are really simple to solve ... But my problem is that I don't want to factorize them myself.

    + I think If I eliminate zeros and then factorize it with current codes, it can be done. but It's a new thing for me and I don't know how to do it properly!
     
  5. Aug 23, 2011 #4

    phyzguy

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    Factoring small numbers like that is really just a process of searching through the possible prime factors up to the square root of the number. You can write a code to do it or use existing codes. Why didn't Wolfram Alpha work for you? It did for me. The example you listed is prime. See this link:

    http://www.wolframalpha.com/input/?i=factor[909091]
     
  6. Aug 23, 2011 #5
  7. Aug 23, 2011 #6
    I did the damn thing, I just entered the non-zero part in Wolfram and factorize the rest of them myself.

    ---
    @Bill Simpson & @phyzguy:
    Of course, if you enter :
    http://www.wolframalpha.com/input/?i=factor(987654320987654321*2^180*5^180

    It will give you the answer, but The numbers weren't in this form and there is not enough room for all the zeros to be entered in Wolfram:
    http://www.wolframalpha.com/input/?...000000000000000000000000000000000000000000000

    , and second, there was 523 of them and That's why I said I want to eliminate all zeros and write a code for them... Because It was a nightmare to enter them one by one, I wanted to give the .ods to that program and get the answers as fast as possible.... anyways, It's done now! :-)
     
  8. Aug 24, 2011 #7

    mathwonk

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    if you ever have a real challenge to factor large numbers, write Carl Pomerance and ask him.
     
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