Euler's totient function

Etymology
.

Proper noun

 * 1)  The function that counts how many integers below a given integer are coprime to it.

Usage notes

 * Usually denoted with the Greek letter phi ($$\phi$$ or $$\varphi$$).

Translations

 * Finnish: Eulerin φ-funktio
 * German: Eulersche Phi-Funktion
 * Icelandic: phi-fall Eulers
 * Italian: funzione phi di Eulero
 * Japanese: オイラーのφ関数
 * Russian: фу́нкция Э́йлера
 * Spanish: función fi de Euler
 * Swedish: Eulers phi-funktion