Euler's totient function
(Mylib/Number/Totient/totient.cpp)

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• Last update: 2021-04-23 23:44:44+09:00
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Operations

Requirements

Notes

Problems

References

Required by

• Tetration (Mylib/Number/tetration.cpp)

Verified with

• test/aoj/NTL_1_D/main.totient.test.cpp
• test/yosupo-judge/tetration_mod/main.test.cpp

Code

#pragma once
#include <cstdint>

namespace haar_lib {
  constexpr int64_t totient(int64_t n) {
    int64_t ret = n;

    for (int64_t i = 2; i * i <= n; ++i) {
      if (n % i == 0) {
        ret -= ret / i;
        while (n % i == 0) n /= i;
      }
    }

    if (n != 1) ret -= ret / n;

    return ret;
  }
}  // namespace haar_lib

#line 2 "Mylib/Number/Totient/totient.cpp"
#include <cstdint>

namespace haar_lib {
  constexpr int64_t totient(int64_t n) {
    int64_t ret = n;

    for (int64_t i = 2; i * i <= n; ++i) {
      if (n % i == 0) {
        ret -= ret / i;
        while (n % i == 0) n /= i;
      }
    }

    if (n != 1) ret -= ret / n;

    return ret;
  }
}  // namespace haar_lib

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