131

This number is a prime.

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The sum of the first one hundred thirty one 131-digit primes is prime. Can you find a larger example like this? [Gaydos]

Not only is 131 the first Honaker prime, but it's also a Sophie Germain prime whose associated safe prime is 263, the second Honaker prime. [Gaydos]

The Collatz trajectory length of 131000. [Gaydos]