Sigma Function of 1

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Example of Sigma Function of Integer

$\map \sigma 1 = 1$

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


By definition, the $\sigma$ function 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.