520

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


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


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

Also see

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