intergers

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saadiagha Junior | Next Rank: 30 Posts
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intergers

Post Fri Dec 21, 2012 11:50 am
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  • Lap #[LAPCOUNT] ([LAPTIME])
    For every even positive integer m,f(m)represents the product of all even integers from 2 to m inclusive. for example f(12)= 2.4.6.8.10.12
    What is the greatest prime factor of f(24)

    I got the correct answer but my working was different. Any ideas if there is more than one correct way of answering this?

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    puneetkhurana2000 Master | Next Rank: 500 Posts Default Avatar
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    Post Fri Dec 21, 2012 2:46 pm
    The answer is 11 because f(24) contains 22(2*11) and 13 is not a possibility.

    saadiagha Junior | Next Rank: 30 Posts
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    Post Fri Dec 21, 2012 2:51 pm
    can I multiply 22.24, since they are the highest integers, and then factorize? Or will I be violating a principle doing that?

    puneetkhurana2000 Master | Next Rank: 500 Posts Default Avatar
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    Post Fri Dec 21, 2012 3:06 pm
    There is no need to do that because even after multiplication and then factorization as suggested by you the greatest prime factor will be 11 only.

    So, I don't see a point.

    E.g.
    Greatest prime factor of 1*2*3 is 3
    or
    Greatest prime factor of 6 (which has 1,2,3,6 as factors) is also 3.

    Hope this makes sense!!!

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