673

Number
$673$ (six hundred and seventy-three) is:


 * The $122$nd prime number


 * The $15$th Proth prime after $3$, $5$, $13$, $17$, $41$, $97$, $113$, $193$, $241$, $257$, $353$, $449$, $577$, $641$:
 * $673 = 21 \times 2^5 + 1$