Problem:
Find the number of positive divisors of such that .
, 2013
Solution
Solution:
Since , we know that for some integer and some integer which is relatively prime to . Consequently, is a divisor of ; eliminating common factors with gives that is a factor of , which has factors. Finally, can be , or , so there are a total of possibilities.
Want a route through all this instead of an archive? The track
puts 2,000 problems in a working order, from AMC 10 level to the IMO shortlist.