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(P/S) What is the biggest prime factor?

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(P/S) What is the biggest prime factor? [#permalink] New post 26 Nov 2007, 05:43
Question)
If <n> means the production of all the positive even numbers until n(including n), what is the Biggest prime factor of <20>+<22>?


How? I have seen similar questions, but still didn't get the right understanding... please help me.
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Re: (P/S) What is the biggest prime factor? [#permalink] New post 26 Nov 2007, 16:42
pretttyune wrote:
Question)
If <n> means the production of all the positive even numbers until n(including n), what is the Biggest prime factor of <20>+<22>?


How? I have seen similar questions, but still didn't get the right understanding... please help me.


<20> = 2*4*6*...*20
<22> = 2*4*6*...*20*22

<20>+<22> = (2*4*6*...*20) + (2*4*6*...*20*22) = (2*4*6*...*20)*(1+22) = (2*4*6*...*20)*23

Since 2 is the only even prime number and no multiplication is greater than 23 and 23 is a prime number, 23 is the answer.
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Re: (P/S) What is the biggest prime factor? [#permalink] New post 26 Nov 2007, 17:00
bkk145 wrote:
pretttyune wrote:
Question)
If <n> means the production of all the positive even numbers until n(including n), what is the Biggest prime factor of <20>+<22>?


How? I have seen similar questions, but still didn't get the right understanding... please help me.


<20> = 2*4*6*...*20
<22> = 2*4*6*...*20*22

<20>+<22> = (2*4*6*...*20) + (2*4*6*...*20*22) = (2*4*6*...*20)*(1+22) = (2*4*6*...*20)*23

Since 2 is the only even prime number and no multiplication is greater than 23 and 23 is a prime number, 23 is the answer.



absolutly agree with 23.
Re: (P/S) What is the biggest prime factor?   [#permalink] 26 Nov 2007, 17:00
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