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