208,335

Number
$208 \, 335$ is:


 * $3 \times 5 \times 17 \times 19 \times 43$


 * The $645$th triangular number:
 * $208 \, 335 = \displaystyle \sum_{k \mathop = 1}^{645} k = \dfrac {645 \times \paren {645 + 1} } 2$


 * The $85$th square pyramidal number:
 * $645 = \displaystyle \sum_{k \mathop = 1}^{85} k^2 = \dfrac {85 \paren {85 + 1} \paren {2 \times 85 + 1} } 6$


 * The $4$th and last after $1$, $55$, $91$ of the $4$ square pyramidal numbers which are also triangular.