n // A being the count of fractions with denominator A where was a key insight I've failed to notice for a long time. I was also thinking "Easy" is crazy for such a problem which takes pages of editorial on the official site.

In retrospect, to begin with this concept in mind, figuring out the removal of fractions in non-reduced form would be straightforward, consider we should have been very familiar with similar techniques from prime sieve, Totient function and more generally, dynamic programming.