# Sigma Function of 3

## Example of Sigma Function of Prime Number

$\map \sigma 3 = 4$

where $\sigma$ denotes the $\sigma$ function.

## Proof

$\map \sigma p = p + 1$

where $p$ is a prime number.

We have that $3$ is a prime number.

Hence:

$\map \sigma 3 = 3 + 1 = 4$

$\blacksquare$