Determine all positive integers such that all positive integers less than and coprime to are powers of primes.
Solution
Notice that is the first index such that . Now, if for some index , then (by Bertrand-Tchebysheff) , so for all indices .
Consequently, , , , and . Examination of the integers less than quickly yields the required numbers: .
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.