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

Fifty-three is the 16th prime number. It is the second balanced prime, and fifth isolated prime.

53 is a sexy prime with 47 and 59. It is the eighth Sophie Germain prime, and the ninth Eisenstein 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 the ninth self number in decimal.^[4]

53 is the smallest prime number that does not divide the order of any sporadic group, inclusive of the six pariahs; it is also the first prime number that is not a member of Bhargava's prime-universality criterion theorem (followed by the next prime number 59), an integer-matrix quadratic form that represents all prime numbers when it represents the sequence of seventeen integers {2, ..., 47, 67, 73}.^[5]

• The atomic number of iodine

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).^[6]
• 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

• 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

• List of highways numbered 53