199

199 is a prime number.

199 is the 11th Lucas number.

197 and 199 form a twin prime pair.

199 is a number that cannot be written as a sum of three squares.

199 is the smallest number with an additive persistence of 3: 1 + 9 + 9 = 19; 1 + 9 = 10; 1 + 0 = 1.

The Cape May Lighthouse in New Jersey has 199 steps in the tower's cast-iron spiral staircase.

Source: Number Gossip