15,251

Number
$15 \, 251$ (fifteen thousand, two hundred and fifty-one) is:


 * $101 \times 151$


 * The $6$th pentagonal number after $1$, $5$, $22$, $1001$, $2882$ which is also palindromic:
 * $15 \, 251 = \displaystyle \sum_{k \mathop = 1}^{101} \left({3 k - 2}\right) = \dfrac {101 \left({3 \times 101 - 1}\right)} 2$