809
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Number
$809$ (eight hundred and nine) is:
- The $140$th prime number.
- The upper end of the $8$th record-breaking gap between twin primes:
- $809 - 661 = 148$
- The $12$th obstinate number after $1$, $127$, $149$, $251$, $331$, $337$, $373$, $509$, $599$, $701$, $757$
- The smaller of the $31$st pair of twin primes:
- $811 - 809 = 2$
- 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.
Also see
- Previous ... Next: Twin Primes
- Previous ... Next: Record Gaps between Twin Primes
- Previous ... Next: Obstinate Number
- Previous ... Next: Sophie Germain Prime
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