# 233 (number)

 ← 232 233 234 →
Cardinal two hundred and thirty-three
Ordinal 233rd
(two hundred and thirty-third)
Factorization 233
Prime yes
Roman numeral CCXXXIII
Binary 111010012
Ternary 221223
Quaternary 32214
Quinary 14135
Senary 10256
Octal 3518
Duodecimal 17512
Vigesimal BD20
Base 36 6H36

233 is the natural number between 232 and 234. It is also a prime number.

## In mathematics

233 is an irregular prime, a full reptend prime, a cousin prime, a Chen prime, a Fibonacci prime and a sexy prime. It is the 13th Fibonacci number. It is an Eisenstein prime of the form $3n - 1$ with no imaginary part. Since 233 × 2 + 1 = 467, another prime, 233 is a Sophie Germain prime. 233 is also a prime triplet (with 227 and 229).

It is the 13th Fibonacci number, being the sum of 89 and 144. Being an odd-indexed Fibonacci number, it is also a Markov number, appearing in solutions to the Markov Diophantine equation: (1, 89, 233), (89, 233, 610), (233, 610, 426389), ... It is also the second (non-trivial) Fibonacci number whose digits and digit sum are also Fibonacci numbers.

In base 10 there is no integer that added up to its own digits yields 233, hence 233 is a self number. In base 3, the sum of 233's digits is composite; no smaller prime has this property.

## In other fields

In current teenage slang and Internet discourse, 233 is sometimes used instead of BFF to abbreviate "Best Friends Forever." The digits correspond to the number keys that would be pressed on a telephone while sending a text message. In Windows live messenger 233 is a commonly used to represent the emoticon of raised eybrows.

The expression "233" is commonly used by Internet users in China to express a meaning similar to that of the Internet discourse LOL. It originated from the 233rd emoticon from the popular Chinese website mop.com, which portrays a figure laughing while banging on the floor.

## In literature

233 is the final chapter of The Curious Incident of the Dog in the Night-Time by Mark Haddon, which uses all prime numbers for its chapters due to its narrator's Asperger's syndrome.