The result of Example 16 suggests that perhaps the matrix
$A=\begin{bmatrix} 1 & \frac{1}{2} & \frac{1}{3} \ \ \cdots \ & \frac{1}{n} \\ \frac{1}{2}& \frac{1}{3} & \cdots & \frac{1}{n+1}\\ \frac{1}{3} & . & \cdots & .\\. & . & \cdots & .\\\frac{1}{n} & \frac{1}{n+1} & \cdots & \frac{1}{2n-1} \end{bmatrix}$
is invertible and $A^{-1}$ has integer entries. Can you prove that?