# Understanding Cryptography by Christof Paar and Jan Pelzl - Chapter 1 Solutions - Ex1.10

- 2 mins- Return to index
- Exercise 1.1
- Exercise 1.2
- Exercise 1.3
- Exercise 1.4
- Exercise 1.5
- Exercise 1.6
- Exercise 1.7
- Exercise 1.8
- Exercise 1.9
- Exercise 1.10
- Exercise 1.11
- Exercise 1.12
- Exercise 1.13
- Exercise 1.14

## Exercise 1.10

Find all integers between that are relatively prime to for . We denote the number of integers which fulfill the condition by , e.g. . This function is called “Euler’s phi function”. What is for ?

### Solution

*I haven’t yet verified this solution independently. If you spot any mistakes, please leave a comment in the Disqus box at the bottom of the page.*

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