Divisor Sum of 4

Example of Divisor Sum of Integer

$\map {\sigma_1} 4 = 7$

where $\sigma_1$ denotes the divisor sum.

Proof

We have that:

$4 = 2^2$

Hence:

\(\ds \map {\sigma_1} 4\)

\(=\)

\(\ds 2 \times 4 - 1\)

Divisor Sum of Power of 2

\(\ds \)

\(=\)

\(\ds 7\)

$\blacksquare$