No Arabic abstract
Nicolas and DeSalvo and Pak proved that the partition function $p(n)$ is log concave for $n geq 25$. Chen, Jia and Wang proved that $p(n)$ satisfies the third order Tur{a}n inequality, and that the associated degree 3 Jensen polynomials are hyperbolic for $n geq 94$. 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 $k geq 2$. In particular, for any positive integers $d$ and $k$, the order $d$ Tur{a}n 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.
For a graph $H$ and a $k$-chromatic graph $F,$ if the Turan graph $T_{k-1}(n)$ has the maximum number of copies of $H$ among all $n$-vertex $F$-free graphs (for $n$ large enough), then $H$ is called $F$-Turan-good, or $k$-Turan-good for short if $F$ is $K_k.$ In this paper, we construct some new classes of $k$-Turan-good graphs and prove that $P_4$ and $P_5$ are $k$-Turan-good for $kge4.$
We present a short, self-contained, and purely combinatorial proof of Linniks theorem: for any $varepsilon > 0$ there exists a constant $C_varepsilon$ such that for any $N$, there are at most $C_varepsilon$ primes $p leqslant N$ such that the least positive quadratic non-residue modulo $p$ exceeds $N^varepsilon$.
This note resolves an open problem asked by Bezrukov in the open problem session of IWOCA 2014. It shows an equivalence between regular graphs and graphs for which a sequence of invariants presents some symmetric property. We extend this result to a few other sequences.
In this paper we consider successive iterations of the first-order differential operations in space ${bf R}^3.$
In recent work, M. Schneider and the first author studied a curious class of integer partitions called sequentially congruent partitions: the $m$th part is congruent to the $(m+1)$th part modulo $m$, with the smallest part congruent to zero modulo the number of parts. Let $p_{mathcal S}(n)$ be the number of sequentially congruent partitions of $n,$ and let $p_{square}(n)$ be the number of partitions of $n$ wherein all parts are squares. In this note we prove bijectively, for all $ngeq 1,$ that $p_{mathcal S}(n) = p_{square}(n).$ Our proof naturally extends to show other exotic classes of partitions of $n$ are in bijection with certain partitions of $n$ into $k$th powers.