  For any positive integer $n$, let $\sigma (n)$ be the sum of all positive
divisors of $n.$ In this paper, it is proved that for every integer $ 1\leq
k\leq 29,\ (k,30)=1, $ we have $$\sum_{n\leq K}\sigma(30n)>\sum_{n\leq
K}\sigma(30n+k)$$ for all $K\in \mathbb{N},$ which gives a positive answer to a
problem posed by Pongsriiam recently.
