111

This number is a composite.

The magic constant for the smallest magic square composed only of prime numbers if 1 were counted as a prime.

111322 + 322111 is prime. [Kulsha]

The number of consecutive composites that follow the prime 370261, the first run of more than 100.

Nayan Hajratwala's home computer, a 350 MHz IBM Aptiva, used 111 days of idle time to find the thirty-eighth Mersenne prime.

1112 + 2 is prime.

111 equals the sum of 2 + 3 + 4 + ... + 17 minus the sum of primes less than 17. [Trotter]

10^(2*55)+111*10^(55-1)+1 is a palindromic prime with 111 digits and 111 as the "center nut" of the number. [Fougeron]

111*10^100+1 is the smallest prime which is one more than a multiple of googol. [Wu]

The smallest palindromic number whose English names contain a prime number of letters. [Russo]

The smallest multidigit palindromic number n such that the number of primes below n^2 does not exceed n times the number of primes below n. [Russo]

The smallest palindromic number n such that the sum of its digits is a prime factor. [Russo]

111 x 2111 - 111 - 2111 is prime. [Noll]

The smallest repunit semiprime. [Gupta]

The smallest tetradic semiprime. Note that this number contains the smallest tetradic prime. [Capelle]

The smallest nontrivial palindromic semiprime. [Silva]

111 is the total number of prime numbers that can be displayed on a 12-hour digital clock. [Ward]

The smallest repunit divisible by an emirp. [Wilson]

The sum of the emirp pair 37 and 73 plus 1 is a repunit, i.e., 37 + 73 + 1 = 111. Additionally, the sum of n of these emirp pairs plus n is also a repdigit, for n = 2 thru 9. [Wiszowaty]

(There are 5 curios for this number that have not yet been approved by an editor.)