121 is the natural number following 120 and preceding 122.
One hundred twenty-one is a square and is the sum of three consecutive primes (37 + 41 + 43). It is also a star number and a centered octagonal number. In base 10, it is a Smith number since its digits add up to the same value as its factorization (which uses the same digits) and as a consequence of that it is a Friedman number. But it can not be expressed as the sum of any other number plus that number's digits, making 121 a self number.
One hundred twenty-one is also:
