21,701

Number
$21 \, 701$ (twenty-one thousand, seven hundred and one) is:


 * The $2435$th prime number


 * The index of the $25$th Mersenne prime after $2$, $3$, $5$, $7$, $13$, $\ldots$, $2203$, $2281$, $3217$, $4253$, $4423$, $9689$, $9941$, $11 \, 213$, $19 \, 937$:
 * $M_{21 \, 701} = 2^{21 \, 701} - 1 \approx 4 \cdotp 487 \times 10^{6532}$