Divisor Sum of 1

Example of Divisor Sum of Integer

 * $\map {\sigma_1} 1 = 1$

where $\sigma_1$ denotes the divisor sum.

Proof
By definition, the divisor sum of an integer $n$ is the sum of the positive integer divisors of $n$.

There is only one positive integer which is a divisor of $1$, and that is $1$ itself.

Hence the result.