How I can tell that $\displaystyle 4k^3+18k^2+28k+15$ is composite for an positive integer $\displaystyle n$?

Thanks!

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- Dec 23rd 2008, 05:51 AMWinding FunctionComposite Expression
How I can tell that $\displaystyle 4k^3+18k^2+28k+15$ is composite for an positive integer $\displaystyle n$?

Thanks! - Dec 23rd 2008, 06:58 AMTwistedOne151Factoring
Consider that $\displaystyle 4k^3+18k^2+28k+15=(2k+3)(2k^2+6k+5)$.

--Kevin C. - Dec 23rd 2008, 06:58 AMIsomorphism
But where is 'n' in the expression? (Evilgrin)

I had to do a fair amount trial and error to figure out the following factorization:

$\displaystyle 4k^3+18k^2+28k+15 = (2k+3)(2k^2 + 6k + 5)$