520

Number
$520$ (five hundred and twenty) is:
 * $2^3 \times 5 \times 13$


 * The smallest positive integer which can be expressed as the sum of $2$ distinct lucky numbers in $28$ different ways


 * The $41$st untouchable number after $2$, $5$, $52$, $88$, $96$, $120$, $124$, $\ldots$, $324$, $326$, $336$, $342$, $372$, $406$, $408$, $426$, $430$, $448$, $472$, $474$, $498$, $516$, $518$


 * The $50$th noncototient after $10$, $26$, $34$, $50$, $\ldots$, $470$, $474$, $482$, $490$, $518$:
 * $\nexists m \in \Z_{>0}: m - \map \phi m = 520$
 * where $\map \phi m$ denotes the Euler $\phi$ function

Also see