This number is a composite.
Every number greater than 121 is the sum of distinct primes of the form 4n + 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]
(There are 4 curios for this number that have not yet been approved by an editor.)
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