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A Greek phi of a number, counting coprime predecessors.
Also known as: Totient function, Euler phi function, Phi function
φ(n) counts how many numbers below n share no factor with it. It is the size of the multiplicative group modulo n, which is why it appears as the exponent in Euler's theorem and, through that, in the RSA key equations.
Denotes the count of positive integers up to n that are coprime to n.
Contexts: Mathematics
Gives the order of the multiplicative group of integers modulo n, which is the group-theoretic content of Euler's theorem.
Contexts: Mathematics
Appears directly in RSA, where the private exponent is computed modulo the totient of the modulus.
Contexts: Mathematics
A Greek lowercase phi — a circle or oval crossed by a vertical stroke extending above and below — followed by a bracketed numeral.