Euler’s totient function counts the number of positive integers up to a given integer **N** that are relatively prime to **N**. Formally, it is the count of integers **K** in range **1 ≤ K ≤ N** for which the greatest common divisor **gcd(N, K)** equal to **1**. It is denoted as **ϕ(N)**.

This is a companion discussion topic for the original entry at https://toph.co/p/story-of-totient-function