\begin{definition}[Definition:Almost Perfect Number/Definition 2]
Let $n \in \Z_{\ge 0}$ be a positive integer.
$n$ is '''almost perfect''' {{iff}}:
:$\map {\sigma_1} n = 2 n - 1$
where $\map {\sigma_1} n$ denotes the divisor sum function of $n$.
\end{definition}