4851

Number
$4851$ (four thousand, eight hundred and fifty-one) is:


 * $3^2 \times 7^2 \times 11$


 * The $21$st pentagonal pyramidal number after $1$, $6$, $12$, $40$, $75$, $126$, $196$, $288$, $405$, $550$, $726$, $936$, $1183$, $1470$, $1800$, $2176$, $2601$, $3078$, $3610$, $4200$:
 * $4851 = \displaystyle \sum_{k \mathop = 1}^{21} \dfrac {k \left({3 k - 1}\right)} 2 = \dfrac {21^2 \left({21 + 1}\right)} 2$