* How fast does the totient function grow? For large <math>n</math>, <math>\phi(n) \approx n</math> "on average". One way to make this precise is by stating <math> \frac{1}{n^2} \sum_{k=1}^n \varphi(k) = \frac{3}{\pi^2} + O \left( \frac{\log n}{n} \right)</math>, while in contrast <math> \frac{1}{n^2} \sum_{k=1}^n k = \frac{1}{2} + O \left( \frac{1}{n} \right). | * How fast does the totient function grow? For large <math>n</math>, <math>\phi(n) \approx n</math> "on average". One way to make this precise is by stating <math> \frac{1}{n^2} \sum_{k=1}^n \varphi(k) = \frac{3}{\pi^2} + O \left( \frac{\log n}{n} \right)</math>, while in contrast <math> \frac{1}{n^2} \sum_{k=1}^n k = \frac{1}{2} + O \left( \frac{1}{n} \right). |