A note on the Higher order Turán inequalities for $k$-regular partitions

Abstract

Nicolas and DeSalvo and Pak proved that the partition function $p(n)$ is log concave for $n\ge 25$. Chen, Jia and Wang proved that $p(n)$ satisfies the third order Turán inequality, and that the associated degree 3 Jensen polynomials are hyperbolic for $n\ge 94$. More recently, Griffin, Ono, Rolen and Zagier proved more generally that for all $d$, the degree $d$ Jensen polynomials associated to $p(n)$ are hyperbolic for sufficiently large $n$. In this paper, we prove that the same result holds for the $k$-regular partition function $p_k(n)$ for $k\ge 2$. In particular, for any positive integers $d$ and $k$, the order $d$ Turán inequalities hold for $p_k(n)$ for sufficiently large $n$. The case when $d=k=2$ proves a conjecture by Neil Sloane that $p_2(n)$ is log concave.