551

Number
$551$ (five hundred and fifty-one) is:


 * $19 \times 29$


 * The $19$th second pentagonal number after $2$, $7$, $15$, $26$, $40$, $57$, $77$, $100$, $126$, $155$, $187$, $222$, $260$, $301$, $345$, $392$, $442$, $495$:
 * $551 = \dfrac {19 \left({3 \times 19 + 1}\right)} 2$