8778

Number
$8778$ (eight thousand, seven hundred and seventy-eight) is:


 * $2 \times 3 \times 7 \times 11 \times 19$


 * The $2$nd of the $8$th pair of triangular numbers whose sum and difference are also both triangular:
 * $7875 = T_{125}$, $8778 = T_{132}$, $8778 + 7875 = T_{182}$, $8778 - 7875 = T_{42}$


 * The $12$th palindromic triangular number after $0$, $1$, $3$, $6$, $55$, $66$, $171$, $595$, $666$, $3003$, $5995$


 * The $132$nd triangular number after $1$, $3$, $6$, $10$, $15$, $\ldots$, $7503$, $7626$, $7750$, $7875$, $8001$, $8128$, $8256$, $8385$, $8515$, $8646$:
 * $8778 = \displaystyle \sum_{k \mathop = 1}^{132} k = \dfrac {132 \times \paren {132 + 1} } 2$