IMO Shortlist 1983 problem 2


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2. travnja 2012.
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Let n be a positive integer. Let \sigma(n) be the sum of the natural divisors d of n (including 1 and n). We say that an integer m \geq 1 is superabundant (P.Erdos, 1944) if \forall k \in  \{1, 2, \dots , m - 1 \}, \frac{\sigma(m)}{m} >\frac{\sigma(k)}{k}.
Prove that there exists an infinity of superabundant numbers.
Izvor: Međunarodna matematička olimpijada, shortlist 1983