5,704,689,200,685,129,054,721

Number
$5 \, 704 \, 689 \, 200 \, 685 \, 129 \, 054 \, 721$ is:


 * The $n$th prime, where $n$ remains to be determined


 * One of the two prime factors of the $8$th Fermat number $2^{\left({2^7}\right)} + 1$, the other being $59 \, 649 \, 589 \, 127 \, 497 \, 217$:
 * $5 \, 704 \, 689 \, 200 \, 685 \, 129 \, 054 \, 721 = 11 \, 141 \, 971 \, 095 \, 088 \, 142 \, 685 \times 2^9 + 1$