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Find about the rational number phi(d)/b

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September 29, 2010
number theoryrelatively primeDivisibilityEulers functionIMO ShortlistIMO Longlist

Problem Statement

(FRA6)(FRA 6) Consider the integer d=ab1cd = \frac{a^b-1}{c}, where a,ba, b, and cc are positive integers and ca.c \le a. Prove that the set GG of integers that are between 11 and dd and relatively prime to dd (the number of such integers is denoted by ϕ(d)\phi(d)) can be partitioned into nn subsets, each of which consists of bb elements. What can be said about the rational number ϕ(d)b?\frac{\phi(d)}{b}?