# 121

This number is a composite.

Every number greater than 121 is the sum of distinct primes of the form 4*n* + 1. [Wells]

The smallest palindromic composite such that some permutation of digits is prime.

121 is the only odd palindromic square with an odd number of digits that is divisible by a palindromic prime number with an even number of digits. [Luhn]

Smallest palindrome pseudoprime to base 3. [De Geest]

A palindrome whose prime factors are palindromic. [Russo]

121 can be expressed as the sum of a prime and its reversal for exactly three distinct primes. [Patterson]

The smallest three-digit number such that the sum of the values that result by placing the exponentation symbol (^) between any two consecutive digits is prime (i.e., 1^21+12^1 is prime.) [Opao]

121, 143, 169, and 187 are the first and possibly only four consecutive brilliant numbers whose reverses are also brilliant numbers. [Gaydos]