+"Euler's Totient Function," often written as φ(_n_), is a fundamental concept in [number theory](/wiki/number_theory). It counts the positive integers less than or equal to a given integer _n_ that are [relatively prime](/wiki/relatively_prime) to _n_. This function elegantly reveals the multiplicative structure underlying a number's set of coprime companions.
+## See also
+- [Modular Arithmetic](/wiki/modular_arithmetic)
+- [Multiplicative Function](/wiki/multiplicative_function)
+- [Prime Number](/wiki/prime_number)
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