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    Daily ChallengeHardNumber Theory

    What is φ(20)\varphi(20)? (Euler's totient)

    Qual é φ(20)\varphi(20)? (Função de Euler)

    Answer options

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    Solution

    φ(20)=20×(1−12)×(1−15)=20×12×45=8\varphi(20) = 20 \times \left(1-\tfrac{1}{2}\right) \times \left(1-\tfrac{1}{5}\right) = 20 \times \tfrac{1}{2} \times \tfrac{4}{5} = 8