3781

Number
$3781$ (three thousand, seven hundred and eighty-one) is:


 * $19 \times 199$


 * The $36$th centered hexagonal number after $1$, $7$, $19$, $37$, $61$, $91$, $127$, $\ldots$, $2791$, $2977$, $3169$, $3367$, $3571$:
 * $3781 = \ds 1 + \sum_{k \mathop = 1}^{36 - 1} 6 k = 36^3 - 35^3$