Divisor sum
= Divisor sum
The divisor sum of an arithmetic function $f$ is
$$
F(n)=\sum_{d\mid n}f(d).
$$
If $f$ is multiplicative, then $F$ is multiplicative as well.
= Divisor sum
The divisor sum of an arithmetic function $f$ is
$$
F(n)=\sum_{d\mid n}f(d).
$$
If $f$ is multiplicative, then $F$ is multiplicative as well.