8001

Number
$8001$ (eight thousand and one) is:


 * $3^2 \times 7 \times 127$


 * The $126$th triangular number after $1$, $3$, $6$, $10$, $15$, $\ldots$, $6786$, $6903$, $7021$, $7140$, $7260$, $7381$, $7503$, $7626$, $7750$, $7875$:
 * $8001 = \displaystyle \sum_{k \mathop = 1}^{126} k = \dfrac {126 \times \paren {126 + 1} } 2$