In mathematics;
Fifty-two is the 5th Bell number and a decagonal number. It is an untouchable number, since it is never the sum of proper divisors of any number, and it is a noncototient since it is never the answer to the equation x - φ(x).

In science;
The atomic number of tellurium

In Astronomy;
Messier object M52, a magnitude 8.0 open cluster in the constellation Cassiopeia

Fifty-two is:
The approximate number of weeks in a year.
A significant number in the Maya calendar.
The number of cards in a standard deck of playing cards.
A comic series from DC Comics entitled 52 has 52 issues.The code for international direct dial phone calls to Mexico.On the piano, the number of white keys.

At age 52:
Fiorello LaGuardia became Mayor of New York.
Alfred Hitchcock directed film Strangers on a Train.
Ray Kroc opened the first McDonald's in Des Plaines, III.

For over twenty years, 52 was the best-known car number of retired NASCAR driver Jimmy Means.

The computer game Deus Ex & Wipeout takes place in 2052.

Manhattan's 52nd Street between 5th and 7th Aves was known as Swing Street during the 1930s and 1940s.

The Reparations Agreement between Israel and West Germany (German: Luxemburger Abkommen, Hebrew: הסכם השילומים) was signed on September 10, 1952.

The number of sons of Nebo in the Census of men of Israel upon return from exile (Holy Bible, Ezra 2:29)

5:2 Then rose up Zerubbabel the son of Shealtiel, and Jeshua the son of Jozadak, and began to build the house of God with the prophets of God helping them.