How do you prove that 1280000401 is a composite number?
Hello, RuyHayabusa!
Now that Ipuchala has factored it, I see a truly far-fetched approach.How do you prove that 1,280,000,401 is a composite number? . I don't know . . .
$\displaystyle 1,280,\!000,\!401 \;=\;2^7(10^7) + 2^2(10^2)+1 \;=\;20^7 + 20^2 + 1$
. . . . . . . . $\displaystyle 421 \;=\;2^2(10^2) + 2(10) + 1 \;=\;20^2 + 20 + 1$
Then: .$\displaystyle (20^7 + 20^2 + 1) \div (20^2+20+1) \;=\;20^5 - 20^4 + 20^2 - 20 + 1$
That is: .$\displaystyle 1,\!280,\!000,\!401 \div 421 \;=\;3,\!040,\!381$