403

Number
$403$ (four hundred and three) is:


 * $13 \times 31$


 * The $13$th heptagonal number after $1, 7, 18, 34, 55, 81, 112, 148, 189, 235, 286, 342$:
 * $403 = 1 + 7 + 11 + 16 + 21 + 26 + 31 + 36 + 41 + 46 + 51 + 56 = \dfrac {13 \left({5 \times 13 - 3}\right)} 2$