121 (number)

In mathematics

• a square
• the sum of the powers of 3 from 0 to 4, so a repunit in ternary. Furthermore, 121 is the only square of the form, where p is prime.
• the sum of three consecutive prime numbers.
• As, it provides a solution to Brocard's problem. There are only two other squares known to be of the form. Another example of 121 being one of the few numbers supporting a conjecture is that Fermat conjectured that 4 and 121 are the only perfect squares of the form .
• It is also a star number, a centered tetrahedral number, and a centered octagonal number.
• In decimal, it is a Smith number since its digits add up to the same value as its factorization and as a consequence of that it is a Friedman number. But it cannot be expressed as the sum of any other number plus that number's digits, making 121 a self number.