1378

Number
$1378$ (one thousand, three hundred and seventy-eight) is:
 * $2 \times 13 \times 53$


 * The $52$nd triangular number after $1$, $3$, $6$, $10$, $15$, $\ldots$, $990$, $1035$, $1081$, $1128$, $1176$, $1225$, $1275$, $1326$:
 * $1378 = \ds \sum_{k \mathop = 1}^{52} k = \dfrac {52 \times \paren {52 + 1} } 2$