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mick t
Lv 5
mick t asked in Science & MathematicsMathematics · 1 decade ago

Is there a fast way to determine if this is a prime number?

12,254,783

3 Answers

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  • Anonymous
    1 decade ago
    Favorite Answer

    Yes, there is. And yes, it is prime.

    http://www.math.com/students/calculators/source/pr...

  • 1 decade ago

    I don't think there's a way to tell, but you can just eliminate the usual factors. Here's how:

    The number doesn't end with an even number. So it's not a multiple of 2.

    If you add up all the digits in the number, and it adds up to a multiple of 3, then the number is a multiple of three. 1+2+2+5+4+7+8+3=32 which is not a multiple of 3. So the number isn't a multiple of three.

    Since it doesn't end with 5 or 0, it can't be a multiple of 5.

    If it's not a multiple of 2 nor 3, it can't be a multiple of 6.

    If it's not a multiple of 2 nor 4, it can't be a multiple of 8.

    If it's not a multiple of 3, it can't be a multiple of 9.

    So that leaves you with it being a multiple of 7, 13, 17,19, etc. You just have to manually divide to check those.

    Hope that helps.

  • TFV
    Lv 5
    1 decade ago

    For large numbers that aren't divisible by anything obvious (2, 3, 5), you end up having to try dividing it by every prime from 2 up to the square root of the number. Even for 3-digit numbers, this can take a long time. For your 8-digit number, forget about it. The only fast way is to run it through a computer program, like the one linked above.

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