6

This number is a composite.

Just showing those entries submitted by 'Firoozbakht': (Click here to show all)

6 + 1, 6 + 66 + 1, 6*66 + 1 , 6 + 66 + 666 + 1 and 6*66*666 + 1 are all primes. [Firoozbakht]

(π(6)*6*6 - 1, π(6)*6*6 + 1 ) are twin primes. [Firoozbakht]

6 is probably the only even number n such that both numbers n^n - (n+1) and n^n + (n+1) are primes. [Firoozbakht]