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Math Help - Proving composite number

  1. #1
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    Proving composite number

    How do you prove that 1280000401 is a composite number?
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  2. #2
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    Re: Proving composite number

    1280000401=421*3040381
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  3. #3
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    Re: Proving composite number

    Hello, RuyHayabusa!

    How do you prove that 1,280,000,401 is a composite number? . I don't know . . .
    Now that Ipuchala has factored it, I see a truly far-fetched approach.


    1,280,\!000,\!401 \;=\;2^7(10^7) + 2^2(10^2)+1 \;=\;20^7 + 20^2 + 1

    . . . . . . . . 421 \;=\;2^2(10^2) + 2(10) + 1 \;=\;20^2 + 20 + 1


    Then: . (20^7 + 20^2 + 1) \div (20^2+20+1) \;=\;20^5 - 20^4 + 20^2 - 20 + 1

    That is: . 1,\!280,\!000,\!401 \div 421 \;=\;3,\!040,\!381
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  4. #4
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    Re: Proving composite number

    Thanks,it really helped!
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