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number of positive divisors of n is second largest divisor of n.

Source: 2023 Czech-Polish-Slovak Match Junior, individual p2 CPSJ

May 5, 2024
number theorynumber of divisors

Problem Statement

For a positive integer nn, let d(n)d(n) denote the number of positive divisors of nn. Determine all positive integers nn for which d(n)d(n) is the second largest divisor of nn.
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