217

Number
$217$ (two hundred and seventeen) is:


 * $7 \times 31$


 * The $9$th centered hexagonal number after $1, 7, 19, 37, 61, 91, 127, 169$:
 * $169 = 1 + 6 + 12 + 18 + 24 + 30 + 36 + 42 + 48 = 9^3 - 8^3$


 * The $13$th number after $1, 3, 22, 66, 70, 81, 94, 115, 119, 170, 210, 214$ whose $\sigma$ value is square: