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Answers for “如何推导 φ(p^k) = p^k − p^{k−1}?”

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For a prime number pp, the only positive divisors are 1 and pp itself. Any integer aa in the range from 1 to pp that is not equal to pp will not share the factor pp.

Conditions: pp is a prime number.; φ(p)\varphi(p) is defined as the count of integers from 1 to pp that are coprime to pp.

Understand why

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Euler's totient function is multiplicative, meaning φ(nm)=φ(n)φ(m)\varphi(nm) = \varphi(n)\varphi(m) whenever gcd⁡(n,m)=1\gcd(n, m) = 1. In the prime factorization of nn, the factors pikip_i^{k_i} are powers of distinct primes.

Conditions: n=p1k1p2k2⋯pmkmn = p_1^{k_1}p_2^{k_2}\cdots p_m^{k_m} is the prime factorization of nn.; pip_i are distinct prime numbers.; φ\varphi is multiplicative for coprime integers.