71 (seventy-one) is the natural number following 70 and preceding 72.

In mathematics

71 is the algebraic degree of Conway's constant, a remarkable number arising in the study of look-and-say sequences.

It is the 20th prime number. The next is 73, with which it composes a twin prime. It is also a permutable prime with 17. If we add up the primes less than 71 (2 through 67), we get 568, which is divisible by 71, 8 times. 71 is the largest (15^th) supersingular prime, which is also a Chen prime. Also, 71² = 7! + 1, making it part of the last known pair of Brown numbers, as (71, 7). It is an Eisenstein prime with no imaginary part and real part of the form 3n – 1. Since 9! + 1 is divisible by 71 but 71 is not one more than a multiple of 9, 71 is a Pillai prime.

As 71 is the least prime factor of one more than the product of the first twenty-two terms of the Euclid–Mullin sequence, it is the twenty-third term. Also, 71 is the largest number which occurs as a prime factor of an order of a sporadic simple group.

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 777 March 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 Judaism

In ancient Israel there was a Sanhedrin headquarters; it had 71 judges who judged cases where the criminal deserved the death penalty.

In other fields

Seventy-one is also:

• The number of different characters that can be used with a standard English Keyboard, excluding uppercase letters.
• 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 , named after U.S. President Theodore Roosevelt.
• The number of the French department Saône-et-Loire.
• The year AD 71, 71 BC, or 1971.
• In the Mexican television sitcom, El Chavo del Ocho, Doña Clotilde lives in the apartment number 71, being therefore known as "Bruja del 71" (Witch of 71).
• Lockheed SR-71 Blackbird long-range, Mach 3 strategic reconnaissance aircraft
• "71 Fragments of a Chronology of Chance," a film by Michael Haneke
• The form number for the United States Office of Personnel Management for requesting a leave of absence.
• Municipal Okrug #71, name of Volkovskoye Municipal Okrug of Frunzensky District of Saint Petersburg, Russia, before 2008
• The Irish Rail 071 Class diesel locomotive.
• In the Jason Bourne novels by American author Robert Ludlum the department within the CIA which made Bourne and the other super agents is called Treadstone Seventy-One.

In sports

• The best-known car number of NASCAR legend Dave Marcis
• Wayne Gretzky scored 71 goals with the Edmonton Oilers in the 1982-83 season
• Barry Bonds hit his 71st home run of 2001 against the Dodgers on October 5, 2001
• NFL Green Bay Packers Bill Forester wore #71
• NFL Dallas Cowboys Mark Tuinei wore #71
• NHL Boston Bruins Davis Payne wore #71
• NHL Nashville Predators J.P. Dumont wears #71
• NHL Pittsburgh Penguins Evgeni Malkin wears #71
• NHL Boston Bruins Jiri Slegr wears #71
• NHL Ottawa Senators Nick Foligno wears #71
• Toronto's Jaskaran "slice" Maur repped 71 reps for the bench test.#71
• The gaolkeeper of the Greek football team Olympiakos Antonis Nikopolidis wears #71