809

Number
$809$ (eight hundred and nine) is:


 * The $140$th prime number.


 * The $35$th Sophie Germain prime after $2$, $3$, $5$, $11$, $23$, $29$, $41$, $\ldots$, $431$, $443$, $491$, $509$, $593$, $641$, $653$, $659$, $683$, $719$, $743$, $761$:
 * $2 \times 809 + 1 = 1619$, which is prime.