Question 2
Exercise 18. The ”Euler’s Totient function” $\varphi(n)$ of a positive integer $n$ is defined as the number of positive integers $m$ less than $n$ such that the highest common factor (HCF) of $m$ and $n$ is 1. For example, $\varphi(12)=4$, since there are 4 numbers $(1,5,7,11)$ less than 12 such that the HCF of 12 and each of these five numbers is 1.
What is the value of $\varphi(51)$?
**Editorial input convention:** Use the definition counting positive integers strictly less than 51. The source example contains a wording typo, explained in the solution.
What is the value of $\varphi(51)$?
**Editorial input convention:** Use the definition counting positive integers strictly less than 51. The source example contains a wording typo, explained in the solution.