52 (fifty-two) is the natural number following 51 and preceding 53.

In mathematics

Fifty-two is

• a composite number; a square-prime, of the form (p², q) where q is a higher prime. It is the sixth of this form and the fifth of the form (2².q).
• the 5th Bell number,^[1] the number of ways to partition a set of 5 objects.
• a decagonal number.^[2]
• with an aliquot sum of 46; within an aliquot sequence of seven composite numbers (52,46,26,16,15, 9,4,3,1,0) to the prime in the 3-aliquot tree. This sequence does not extend above 52 because it is,
• an untouchable number, since it is never the sum of proper divisors of any number,^[3] and it is a noncototient since it is not equal to x − φ(x) for any x.^[4]
• a vertically symmetrical number.^[5]

In science

• The atomic number of tellurium

Astronomy

• Messier object M52, a magnitude 8.0 open cluster in the constellation Cassiopeia, also known as NGC 7654.
• The New General Catalogue object NGC 52, a spiral galaxy in the constellation Pegasus.

In other fields

Fifty-two is:

• The approximate number of weeks in a year. 52 weeks is 364 days, while the tropical year is 365.24 days long. According to ISO 8601, most years have 52 weeks while some have 53.
• A significant number in the Maya calendar
• On the modern piano, the number of white keys (notes in the C major scale)
• The number of cards in a standard deck of playing cards, not counting Jokers or advertisement cards
• The name of a practical joke card game 52 Pickup
• 52 Pick-Up is a film starring Roy Scheider and Ann Margaret
• The code for international direct dial phone calls to Mexico
• A weekly comic series from DC Comics entitled 52 has 52 issues, with a plot spanning one full year.
• The New 52 is a 2011 revamp and relaunch by DC Comics of its entire line of ongoing monthly superhero books.
• The number of letters in the English alphabet, if majuscules are distinguished from minuscules
• The number of the French department Haute-Marne
• 52nd Street (disambiguation)
• 52 Hand Blocks, a variant of the martial art jailhouse rock.
• 52 is the car number of retired NASCAR driver Jimmy Means
• 52 American hostages were held in the Iran hostage crisis
• The number of the laps of the British Grand Prix since 2010.

Historical years

52 BC, AD 52, 1052, 1952 etc.