71 (number) - Definition and Overview

71 is the natural number following 70 and preceding 72.

In mathematics

It is the 20th prime number. The next is seventy-three, with which it comprises a twin prime. It is also a permutable prime with seventeen. If we add up the primes less than 71 (2 through 67), we get 568, which is divisible by 71, 8 times.

71 is a centered heptagonal number.

In science

• The atomic number of lutetium, a lanthanide

In astronomy,

Messier object M71, a magnitude 8.5 globular cluster in the constellation Sagitta

The New General Catalogue object (http://www.ngcic.org/) NGC 71, a magnitude 13.2 peculiar 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 -702 October 8 and ended on 777March 14. The duration of Saros series 71 was 1478.4 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 -472 June 4 and ended on 808 July 11. The duration of Saros series 71 was 1280.1 years, and it contained 72 lunar eclipses.

In other fields

Seventy-one is also:

• The designation of USA Interstate 71, which runs from Kentucky to Ohio.
• The registry of the U.S. Navy's nuclear aircraft carrier USS Theodore Roosevelt (CVN-71), named after U.S. President Theodore Roosevelt.
• The number of the French department Saône-et-Loire.
• The year AD 71, 71 BC, or 1971.