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- Feb 14, 2012

- 3,756

Prove that the number $9999999+1999000$ is composite.

- Thread starter anemone
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- Thread starter
- Admin
- #1

- Feb 14, 2012

- 3,756

Prove that the number $9999999+1999000$ is composite.

- Mar 31, 2013

- 1,322

So we get

$9999999+1999000 = 10^7-1 + 1999 * 1000$

$= 10 * 10^ 6 - 1+ (2000-1)* 1000$

$= 10 x^2 - 1 + (2x-1) x$ putting 1000 = x

$=12x^2 - x - 1$

$= (4x+1)(3x-1)$

$= 4001 * 2999$ putting back x = 1000

Hence it is composite

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