3781

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


 * $19 \times 199$


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