Is $\sum_{r=1}^nrx^{r-1}$ always irreducible (over the integers)? [duplicate]
In the article Classes of polynomials having only one non-cyclotomic irreducible factor the authors (A. Borisov, M. Filaseta, T. Y. Lam, and O. Trifonov) had proved for any $\epsilon > 0$ for all but $O(t^{(1/3)+\epsilon})$ positive integers $n\leq t$, the derivative of the polynomial $f(x)= 1+ x + x^2 + \cdots + x^n$ is irreducible, and in general for all $n\in \mathbb N$ they conjectured $f'(x)$ is irreducible.