369

Number
$369$ (three hundred and sixty-nine) is:


 * $3^2 \times 41$


 * The number of distinct free octominoes


 * The magic constant of a magic square of order $9$, after $1$, $(5)$, $15$, $34$, $65$, $111$, $175$, $260$:
 * $369 = \displaystyle \dfrac 1 9 \sum_{k \mathop = 1}^{9^2} k = \dfrac {9 \paren {9^2 + 1} } 2$

Also see

 * 369 Octominoes