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What is the largest prime number of 4^(17) - 2^(28) ???

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What is the largest prime number of 4^(17) - 2^(28) ??? [#permalink] New post 21 Mar 2007, 13:39
What is the largest prime number of 4^(17) - 2^(28) ???
Thanks guys
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 [#permalink] New post 21 Mar 2007, 13:44
7 for me :)

4^(17) - 2^(28)
= 2^(34) - 2^(28)
= 2^(28) * (2^6 - 1)
= 2^(28) * (2^3 - 1) * (2^3 + 1)
= 2^(28) * (8 - 1) * (8 + 1)
= 2^(28) * (7) * (3 * 3)
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Re: Prime number question [#permalink] New post 21 Mar 2007, 14:20
tlntd177 wrote:
What is the largest prime number of 4^(17) - 2^(28) ???
Thanks guys


is it prime factor?
If yes then is it 7?
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 [#permalink] New post 21 Mar 2007, 17:15
(4^17) - (2^28)

= [(2^2)^17] - (2^28)

= (2^34) - (2^28)

= 2^28[(2^6)-1]

= 2^28(64-1)

= 2^28(63)

63 = 7 x (3^2)

Therefore, 7.
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2 more questions attached [#permalink] New post 21 Mar 2007, 22:21
Hey Guys thanks... I posted 2 more questions...
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2 more questions attached   [#permalink] 21 Mar 2007, 22:21
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What is the largest prime number of 4^(17) - 2^(28) ???

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