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
- The Saros number of the solar eclipse series which began on August 26, 1295 BC and ended on February 21, 220. The duration of Saros series 53 was 1514.5 years, and it contained 85 solar eclipses.
- The Saros number of the lunar eclipse series which began on June 5, 993 BC and ended on July 12, 287 . The duration of Saros series 53 was 1280.1 years, and it contained 72 lunar eclipses.
In other fields
- The racing number of Herbie, a fictional Volkswagen Beetle with a mind of his own, first appearing in the 1969 film The Love Bug
- The code for international direct dial phone calls to Cuba
- Municipal Okrug 53, name of Narodny Municipal Okrug, a municipal okrug of Nevsky District of Saint Petersburg, Russia, until January 2013
- "53 Days" is a northeastern USA rock band
- Part of the title of the 1912 movie North of Fifty Three, remade in 1917
- "53 Days" a novel by Georges Perec
- Ringo Starr’s book "Postcards From the Boys" (2003) contains 53 postcards from fellow Beatles
- 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
- "53 Miles West of Venus” by The B-52's
- EK53 is an Estonian graffiti crew
- The number of the department in France called Mayenne
- Year identifier used on motor vehicles registered in the UK between 1 September 2003 and 28 February 2004
- 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
- Racing numbers of F1 Stockcars (UK) racer John Lund and F1 driver Alexander Rossi
- 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
- Retired jersey number of former Utah Jazz basketball player Mark Eaton
- Retired jersey number of former Los Angeles Dodgers baseball player Don Drysdale
- (sequence A045345 in OEIS)
- Puzzle 31.- The Average Prime number, APN(k) = S(Pk)/k from The Prime Puzzles & Problems Connection website