Divisor Sum of 3

Example of Divisor Sum of Prime Number

$\map {\sigma_1} 3 = 4$

where ${\sigma_1}$ denotes the divisor sum.

Proof

From Divisor Sum of Prime Number:

$\map {\sigma_1} p = p + 1$

where $p$ is a prime number.

We have that $3$ is a prime number.

Hence:

$\map {\sigma_1} 3 = 3 + 1 = 4$

$\blacksquare$

Sources

• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): sigma function (sum function)