2,305,843,009,213,693,951

Number
$2 \, 305 \, 843 \, 009 \, 213 \, 693 \, 951$ is:


 * A prime number


 * The $9$th Mersenne prime after $3$, $7$, $31$, $127$, $8191$, $131 \, 071$, $524 \, 287$, $2 \, 147 \, 483 \, 647$:
 * $2 \, 305 \, 843 \, 009 \, 213 \, 693 \, 951 = 2^{61} - 1$