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 NGC 71 , a magnitude 13.2 peculiar spiral galaxy in the constellation Andromeda

The Saros number 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 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.
• A sexual position similar to 69, but with two fingers in the anus.