1111

This number is a composite.

The concatenation of the prime number 11 with itself.

1111 equals 11² + 12² + 13² + 14² + 15² + 16². [De Geest]

1111 = 11 * 101 in both base 10 and base 2. Notice the factors (11 and 101) are palindromic primes in both of these bases. [Shafer]

The sum of the digits of the first 100 primes. [Wilson]

The smallest tetradic semiprime with tetradic factors. [Capelle]

The smallest repunit number with anti-Yarborough prime factors (101 × 11) whose concatenation (10111) is prime. [Loungrides]

Smallest and only known repunit Smith number, as of 6 January 2022. [Gupta]