21,701

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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 $2$, $3$, $5$, $7$, $13$, $\ldots$, $2203$, $2281$, $3217$, $4253$, $4423$, $9689$, $9941$, $11 \, 213$, $19 \, 937$:

$M_{21 \, 701} = 2^{21 \, 701} - 1 \approx 4 \cdotp 487 \times 10^{6532}$

Also see

• Previous  ... Next: Index of Mersenne Prime
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Historical Note

The Mersenne number $M_{21 \, 701} = 2^{21 \, 701} - 1$ was demonstrated to be a Mersenne prime on $30$ October $1978$, by two $18$-year-old school students: Landon Curt Noll and Ariel Nickel.

Sources

• 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $2^{21701} - 1$
• 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $2^{21,701} - 1$