IMO Shortlist 2005 problem N5
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Avg: 8,0 Denote by the number of divisors of the positive integer . A positive integer is called highly divisible if for all positive integers .
Two highly divisible integers and with are called consecutive if there exists no highly divisible integer satisfying .
(a) Show that there are only finitely many pairs of consecutive highly divisible
integers of the form with .
(b) Show that for every prime number there exist infinitely many positive highly divisible integers such that is also highly divisible.
Two highly divisible integers and with are called consecutive if there exists no highly divisible integer satisfying .
(a) Show that there are only finitely many pairs of consecutive highly divisible
integers of the form with .
(b) Show that for every prime number there exist infinitely many positive highly divisible integers such that is also highly divisible.
Izvor: Međunarodna matematička olimpijada, shortlist 2005