Definition:Aliquot Sum

Definition
Let $n \in \Z$ be a positive integer.

The aliquot sum of $n$ is defined as the sum of its proper divisors, or aliquot parts.

Also known as
The aliquot sum of a positive integer is also known as the more unwieldy and hence uglier term restricted divisor function.

While the term aliquot part is considered archaic nowadays, it has the advantage of being short and euphonious.

Also see

 * Definition:Untouchable Number