53 (fifty-three) is the natural number following 52 and preceding 54. It is the 16th prime number.

In mathematics

• Fifty-three is the 16th prime number. It is also an Eisenstein prime, an isolated prime, a balanced prime and a Sophie Germain prime.^[1]
• The sum of the first 53 primes is 5830, which is divisible by 53, a property shared by only a few other numbers.^[2][3]
• 53 cannot be expressed as the sum of any integer and its decimal digits, making 53 a self number.^[4]
• 53 is the smallest prime number that does not divide the order of any sporadic group.

In science

• The atomic number of iodine

Astronomy

• Messier object M53, a magnitude 8.5 globular cluster in the constellation Coma Berenices
• The New General Catalogue object NGC 53, a magnitude 12.6 barred spiral galaxy in the constellation Tucana

In other fields

Fifty-three is:

• The racing number of Herbie, a fictional Volkswagen Beetle with a mind of his own, first appearing in the 1968 film The Love Bug
• The code for international direct dial phone calls to Cuba
• 53 Days is a northeastern US rock band
• 53 Days a novel by Georges Perec
• In How the Grinch Stole Christmas!, and its animated TV special adaptation, the Grinch says he has put up with the Whos' Christmas cheer for 53 years.
• Fictional 53rd Precinct in the Bronx was found in the TV comedy "Car 54, Where Are You?"
• "53rd & 3rd" a song by the Ramones
• The number of Hail Mary beads on a standard, five decade Catholic Rosary (the Dominican Rosary).^[5]
• The number of bytes in an Asynchronous Transfer Mode packet.
• UDP and TCP port number for the Domain Name System protocol.
• 53-TET (53 tone, equal temperament) is a musical temperament that has a fifth that is closer to pure than our current system.
• 53 More Things To Do In Zero Gravity is a fictional book mentioned in The Hitchhiker's Guide to the Galaxy

Sports

• The maximum number of players on a National Football League roster
• Most points by a rookie in an NBA playoff game, by Philadelphia's Wilt Chamberlain, 1960
• Most field goals (three-game series, NBA playoffs), by Michael Jordan, 1992