819

Number
$819$ (eight hundred and nineteen) is:


 * $3^2 \times 7 \times 13$


 * The $13$th square pyramidal number after $1$, $5$, $14$, $30$, $55$, $91$, $140$, $204$, $285$, $385$, $506$, $650$:
 * $819 = \ds \sum_{k \mathop = 1}^{13} k^2 = \dfrac {13 \paren {13 + 1} \paren {2 \times 13 + 1} } 6$