The Euler function $\phi:\mathbb N\to\mathbb N$ is an arithmetic function $\phi(n)$ counts how many numbers in the subset of natural numbers $\{1,2,\ldots,n\}$ are co-prime to $n.$
The $\phi$ function was first described by Leonhard Euler (1707 - 1783). It can be visualized using SageMath. If you click on the evaluate button, you will see the values of $\tau(n)$ for $n=1,\ldots,100.$
Definitions: 1
Examples: 2
Proofs: 3 4 5
Propositions: 6 7
Sections: 8
Theorems: 9
