280

Number
$280$ (two hundred and eighty) is:


 * $2^3 \times 5 \times 7$


 * The $10$th octagonal number, after $1, 8, 21, 40, 65, 96, 133, 176, 225$:
 * $280 = 1 + 7 + 13 + 19 + 25 + 31 + 37 + 43 + 49 + 55 = 10 \left({3 \times 10 - 2}\right)$