Divisor Sum of Integer/Examples/12

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Example of Divisor Sum of Integer

$\map {\sigma_1} {12} = 28$

where $\sigma_1$ denotes the divisor sum function.


Proof

We have that:

$12 = 2^2 \times 3$


Hence:

\(\ds \map {\sigma_1} {12}\) \(=\) \(\ds \frac {2^3 - 1} {2 - 1} \times \paren {3 + 1}\) Divisor Sum of Integer
\(\ds \) \(=\) \(\ds \frac 7 1 \times 4\)
\(\ds \) \(=\) \(\ds 7 \times 4\)
\(\ds \) \(=\) \(\ds 28\)

$\blacksquare$