297

This number is a composite.

Twenty-nine 7's followed by seven 29's as well as seven 29's followed by twenty-nine 7's are both primes of length 7+29+7. [De Geest]

2*297 + 9*297 + 7*297 + 1 is prime. [Patterson]

Twenty-nine 29's followed by seven 7's is prime. [De Geest]

The number of numbers under one thousand such that the average of their prime factors (with multiplicity) is prime is 297. Note that 297 is one of these, e.g., 297 = 3*3*3*11 and (3+3+3+11)/4 is a prime). [Merickel]

297*2⁵⁴⁶ +/- 1 are twin primes. [Luen]