691

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Number

$691$ (six hundred and ninety-one) is:

The $125$th prime number.

The larger of the $8$th pair of primes whose prime gap is $8$:

$691 - 683 = 8$

The smaller of the $11$th pair of primes whose prime gap is $10$:

$701 - 691 = 10$

The $7$th candidate Lychrel number.

Also see

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