72 (number) - Definition and Overview

72 is the natural number following 71 and preceding 73.

In mathematics

Seventy-two is the sum of four consecutive primes (13 + 17 + 19 + 23), as well as the sum of six consecutive primes (5 + 7 + 11 + 13 + 17 + 19). 72 is a Harshad number and a pronic number.

In normal space, the exterior angles of an equilateral pentagon measure 72 degrees each.

There are 17 solutions to the equation φ(x) = 72, more than any integer below 72, making it a highly totient number.

In science

• The atomic number of hafnium

In astronomy,

Messier object M72, a magnitude 10.0 globular cluster in the constellation Aquarius

The New General Catalogue object (http://www.ngcic.org/) NGC 72, a magnitude 13.5 barred spiral galaxy in the constellation Andromeda

The Saros number (http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros1-175.html) of the solar eclipse series which began on -727 August 16 and ended on 752 January 21. The duration of Saros series 72 was 1478.1 years, and it contained 83 solar eclipses.

The Saros number (http://sunearth.gsfc.nasa.gov/eclipse/LEsaros/LEsaros1-175.html) of the lunar eclipse series which began on -407 June 5 and ended on 891 July 25. The duration of Saros series 72 was 1298.1 years, and it contained 73 lunar eclipses.

In other fields

Seventy-two is also:

• The number of hours in three days.
• The total number of books in the Holy Bible in the Catholic version if the Book of Lamentations is considered part of the Book of Jeremiah.
• In dpi, the standard resolution of an Apple Macintosh screen.
• The number of the French department Sarthe.
• The designation of USA Interstate 72, a freeway that runs from Missouri to Illinois.
• The registry of the U.S. Navy's nuclear aircraft carrier USS Abraham Lincoln (CVN-72), named after U.S. President Abraham Lincoln.
• The designation of the Soviet T-72 tank.
• In the movie The Red Violin, the lot number of the Bussotti red violin at the DuVal auction house.
• The year AD 72, 72 BC, or 1972.