How I can tell that $\displaystyle 4k^3+18k^2+28k+15$ is composite for an positive integer $\displaystyle n$?
Thanks!
But where is 'n' in the expression?
I had to do a fair amount trial and error to figure out the following factorization:
$\displaystyle 4k^3+18k^2+28k+15 = (2k+3)(2k^2 + 6k + 5)$