When factoring a number like (37^3-1)/36 = 3*7*67, 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 (79^3-1)/78 = 3*7^2*43 and 43 < 79 so one example is x = 79, a = 3. My math education level is first year of high school so a transparent explanation, if possible, would be great. I understand basic congruences.