Browse · MATH
Printjmc
number theory senior
Problem
Let How many positive integer divisors of are less than but do not divide ?
Solution
We know that must have factors by its prime factorization. If we group all of these factors (excluding ) into pairs that multiply to , then one factor per pair is less than , and so there are factors of that are less than . There are factors of , which clearly are less than , but are still factors of . Therefore, using complementary counting, there are factors of that do not divide .
Final answer
589