- Thread starter
- Moderator
- #1

- Jun 20, 2014

- 1,925

-----

Give a proof of the number-theoretic equation $$\sum_{d|n} \phi(d) = n$$ where $\phi(d)$ is the number of positive integers $\le d$ and relatively prime to $d$.

-----

Remember to read the POTW submission guidelines to find out how to submit your answers!