 Totient summatory function

The Totient summatory function, often denoted as \( S(n) \), is a mathematical function that sums the values of the Euler's totient function \( \phi(k) \) for all integers \( k \) from 1 to \( n \). The Euler’s totient function \( \phi(k) \) counts the number of positive integers up to \( k \) that are relatively prime to \( k \) (i.e.