# 121 number

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121 is the natural number following 120 and preceding 122.

 Template:Numbers 120s Cardinal One hundred [and] twenty-one Ordinal 121st Factorization ${\displaystyle 11^{2}}$ 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 ${\displaystyle 1+p+p^{2}+p^{3}+p^{4}}$, 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: