Divisor Sum of 2

Example of Sigma Function of Prime Number

 * $\map \sigma 2 = 3$

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

Proof
From Sigma Function of Prime Number:
 * $\map \sigma p = p + 1$

where $p$ is a prime number.

We have that $2$ is a prime number.

Hence:
 * $\map \sigma 2 = 2 + 1 = 3$

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