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For each divisor d> 1 of n, then (d - 1) is a divisor of (n - 1|)

Source: Czech-Polish-Slovak Junior Match 2015, Individual p5 CPSJ

March 15, 2020
divisornumber theory

Problem Statement

Determine all natural numbersn>1 n> 1 with the property: For each divisor d>1d> 1 of number nn, then d−1d - 1 is a divisor of n−1n - 1.
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