- Fifty-three is the 16th prime number. It is also an Eisenstein prime, and a Sophie Germain prime.
- The sum of the first 53 primes is 5830, which is divisible by 53, a property shared by few other numbers.
- 53 written in hexadecimal is 35, that is, the same characters used in the decimal representation, but reversed. Four multiples of 53 share this property: 371 = 17316, 5141 = 141516, 99481 = 1849916, and 8520280 = 82025816, and these are the only numbers that do.
- 53 cannot be expressed as the sum of any integer and its base-10 digits, making 53 a self number.
- 53 is the smallest prime number that does not divide the order of any sporadic group.
- 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
- 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 USA rock band
- "53 Days" a novel by Georges Perec
- In How the Grinch Stole Christmas!, and its animated TV special the Grinch says he's put up with the who's 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).
- 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 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
- "Sloane's A005384 : Sophie Germain primes". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30.
- (sequence A045345 in the OEIS)
- Puzzle 31.- The Average Prime number, APN(k) = S(Pk)/k from The Prime Puzzles & Problems Connection website
- "Sloane's A003052 : Self numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30.