Definition:Almost Perfect Number/Definition 2
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Definition
Let $n \in \Z_{\ge 0}$ be a positive integer.
$n$ is almost perfect if and only if:
- $\map {\sigma_1} n = 2 n - 1$
where $\map {\sigma_1} n$ denotes the divisor sum function of $n$.
Sequence
The sequence of almost perfect numbers begins:
- $1, 2, 4, 8, 16, 32, 64, 128, \ldots$