364

Number
$364$ (three hundred and sixty-four) is:


 * $2^2 \times 7 \times 13$


 * The $12$th tetrahedral number, after $1, 4, 10, 20, 35, 56, 84, 120, 165, 220, 286$:
 * $364 = \displaystyle \sum_{k \mathop = 1}^{12} \frac {k \left({k + 1}\right)} 2 = \dfrac {12 \left({12 + 1}\right) \left({12 + 2}\right)} 6$
 * Hence the total number of gifts in The Twelve Days of Christmas.


 * The $21$st number whose $\sigma$ value is square: