Definition:Almost Perfect Number/Definition 1

Definition

Let $n \in \Z_{\ge 0}$ be a positive integer.

Let $A \left({n}\right)$ denote the abundance of $n$.

$n$ is almost perfect if and only if $A \left({n}\right) = -1$.

Sequence

The sequence of almost perfect numbers begins:

$1, 2, 4, 8, 16, 32, 64, 128, \ldots$