Definition:Deficient Number/Definition 2

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Definition

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


Let $\map {\sigma_1} n$ be the divisor sum function of $n$.

$n$ is deficient if and only if:

$\dfrac {\map {\sigma_1} n} n < 2$


Sequence

The sequence of deficient numbers begins:

$2, 3, 4, 5, 7, 8, 9, 10, 11, 13, 14, 15, 16, 17, 19, 21, \ldots$


Also see