206

This number is a composite.

The numbers 6*206+1, 12*206+1, and 18*206+1 are all prime and hence (6*206+1)*(12*206+1)*(18*206+1) is a Carmichael number. [Patterson]

206 is the smallest number m such that 111^111 + m is prime. [Firoozbakht]

206^0 + 206^1+ 206^2 + 206^3 + 206^4 + 206^5 + 206^6 is a prime number. [Raghava]

206+206^2 +/- 1 is a twin prime pair. [Raghava]