208,335

Number
$208 \, 335$ is:


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


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


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


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