where $X$ is an odd prime, and $a$ is an odd integer.
For example, let $X = 37$, $a = 3$, we get $\frac{37^3-1}{36} = 3 \times 7 \times 67.$ When factoring numbers such as this, I've noticed that almost all have at least one prime factor larger than $X$ (e.g. 67 > 37). I would like to know for what values of $X$, $a$ are ALL of the prime factors of $(X^a-1)/(X-1)$ less than $X$. For example, let $X = 79$, $a = 3$, we get $\frac{79^3-1}{78} = 3 \times 7^2 \times 43$ and $43 < 79$.
My math education level is first year of high school so a transparent explanation, if possible, would be great. I understand basic congruences.