9931
This number is a prime.
The largest 4-digit super-2 emirp. [Loungrides]
The larger prime of any twin prime pair can be expressed as P + 2n^2,
where P is any prime. Having checked up to 9931, all twin
primes up to 10^5, they can also be expressed as P =
2n^2 - Q, where P is the larger of any twin prime pair and Q is
the larger of another twin prime. Can you find a counterexample to this? [Homewood]
Printed from the PrimePages <primes.utm.edu> © G. L. Honaker and Chris K. Caldwell