Published online by Cambridge University Press: 19 May 2022
Let $a,b$ and n be positive integers and let
$S=\{x_1, \ldots , x_n\}$ be a set of n distinct positive integers. For
${x\in S}$, define
$G_{S}(x)=\{d\in S: d<x, \,d\mid x \ \mathrm {and} \ (d\mid y\mid x, y\in S)\Rightarrow y\in \{d,x\}\}$. Denote by
$[S^a]$ the
$n\times n$ matrix having the ath power of the least common multiple of
$x_i$ and
$x_j$ as its
$(i,j)$-entry. We show that the bth power matrix
$[S^b]$ is divisible by the ath power matrix
$[S^a]$ if
$a\mid b$ and S is gcd closed (that is,
$\gcd (x_i, x_j)\in S$ for all integers i and j with
$1\le i, j\le n$) and
$\max _{x\in S} \{|G_S (x)|\}=1$. This confirms a conjecture of Shaofang Hong [‘Divisibility properties of power GCD matrices and power LCM matrices’, Linear Algebra Appl. 428 (2008), 1001–1008].