191

191 is a prime number. It is a Sophie Germain prime because 2 x 191 + 1 = 383 is also a prime. In addition, the resulting number is a palindrome.

191 and 193 form a twin prime pair.

191 is the maximum number of regions into which 19 lines divide the plane.

191 is the smallest palindromic prime whose digit sum (1 + 9 + 1 = 11) is a multidigit palindromic prime. It is also the smallest multidigit palindromic prime that yields a palindrome when multiplied by the next prime: 191 x 193 = 36863.

191 is the smallest prime in a set of four consecutive primes (191, 193, 197, 199) whose sum of digits is another set of four primes (11, 13, 17, 19).

The common U.S. coins--a silver dollar, half-dollar, quarter, dime, nickel, and penny--add up to 191 cents.

Source: Number Gossip