Sum-of-divisors function
= Sum-of-divisors function
{title2=$\sigma_1(n)$}
The sum-of-divisors function is
$$
\sigma_1(n)=\sum_{d\mid n}d.
$$
It is the <divisor sum> of the identity arithmetic function $n\mapsto n$.
= Sum-of-divisors function
{title2=$\sigma_1(n)$}
The sum-of-divisors function is
$$
\sigma_1(n)=\sum_{d\mid n}d.
$$
It is the <divisor sum> of the identity arithmetic function $n\mapsto n$.