3997

Number
$3997$ (three thousand, nine hundred and ninety-seven) is:


 * $7 \times 571$


 * The $37$th centered hexagonal number after $1$, $7$, $19$, $37$, $61$, $91$, $127$, $\ldots$, $2791$, $2977$, $3169$, $3367$, $3571$, $3781$:
 * $3997 = \ds 1 + \sum_{k \mathop = 1}^{37 - 1} 6 k = 37^3 - 36^3$