11

This number is a prime.

11 is the first member of the only prime triplet {11, 13, 17}, where each prime member of this triplet is also a member of 3 different prime triplets: 11 → {5, 7, 11}, {7,11, 13}, {11, 13, 17}, 13 → {7,11, 13}, {11, 13, 17}, {13,17, 19}, 17 → {11, 13, 17}, {13, 17, 19}, {17, 19, 23}. [Green]