MathDB

N2

Part of 2016 Balkan MO Shortlist

Problems(1)

d(n) is the largest divisor of the odd number n, different from n

Source: Balkan BMO Shortlist 2016 N2

7/30/2019
Find all odd natural numbers nn such that d(n)d(n) is the largest divisor of the number nn different from nn. (d(n)d(n) is the number of divisors of the number n including 11 and nn ).
divisormaximumnumber theoryoddIMO Shortlist