165

Number
$165$ (one hundred and sixty-five) is:


 * $3 \times 5 \times 11$


 * The $9$th tetrahedral number, after $1, 4, 10, 20, 35, 56, 84, 120$:
 * $165 = 1 + 3 + 6 + 10 + 15 + 21 + 28 + 36 + 45 = \dfrac {9 \left({9 + 1}\right) \left({9 + 2}\right)} 6$


 * The $1$st of the $2$nd ordered triple of consecutive integers after $\left({105, 106, 107}\right)$ that have Euler $\phi$ values which are strictly increasing:
 * $\phi \left({165}\right) = 80$, $\phi \left({166}\right) = 82$, $\phi \left({167}\right) = 166$