In mathematics, the Riemann hypothesis is a conjecture that the Riemann zeta function has its zeros only at the negative even integers and complex numbers with real part $\frac{1}{2}$. In 1915, Ramanujan proved that under the assumption of the Riemann hypothesis, the inequality $\sigma(n) < e^{\gamma } \times n \times \log \log n$ holds for all sufficiently large $n$, where $\sigma(n)$ is the sum-of-divisors function and $\gamma \approx 0.57721$ is the Euler-Mascheroni constant. In 1984, Guy

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... in proved that the inequality is true for all $n > 5040$ if and only if the Riemann hypothesis is true. Since then, this is called as the Robin inequality. It is known that the Robin inequality is satisfied for many classes of numbers. We show more classes of numbers for which the Robin inequality is always satisfied.