2501

Number
$2501$ (two thousand, five hundred and one) is:


 * $41 \times 61$


 * The $41$st pentagonal number after $1$, $5$, $12$, $22$, $35$, $\ldots$, $1820$, $1926$, $2035$, $2147$, $2262$, $2380$:
 * $2501 = \displaystyle \sum_{k \mathop = 1}^{41} \left({3 k - 2}\right) = \dfrac {41 \left({3 \times 41 - 1}\right)} 2$