# 121 number

**121** is the natural number following 120 and preceding 122.

Template:Numbers 120s | |

Cardinal | One hundred [and] twenty-one |

Ordinal | 121st |

Factorization | |

Roman numeral | CXXI |

Binary | 1111001 |

Hexadecimal | 79 |

**One hundred twenty-one** is a square and is the sum of three consecutive primes (37 + 41 + 43). There are no squares besides 121 known to be of the form , where *p* is prime (3, in this case). There are only two other squares known to be of the form n! + 1.

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:

- The number for voicemail for mobile phones on the Vodafone network
- The model number of the Lockheed EC-121, now on display at the Air Force Museum.
- The year AD 121 or 121 BC.

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