# Math Help - Proving composite number

1. ## Proving composite number

How do you prove that 1280000401 is a composite number?

2. ## Re: Proving composite number

1280000401=421*3040381

3. ## 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: . $1,\!280,\!000,\!401 \div 421 \;=\;3,\!040,\!381$

4. ## Re: Proving composite number

Thanks,it really helped!