Answer to Question #272608 in Combinatorics | Number Theory for Prathibha Rose

Question

Find all integers such that n=12

Answer 1

Euler's totient function $\varphi (n)$  counts the positive integers up to a given integer n that are relatively prime to n

the integers n for which $\varphi (n)=12$ :

$13, 21, 26, 28, 36, 42$