47 (forty-seven) is the natural number following 46 and preceding 48. It is a prime number.

In mathematics

Forty-seven is the fifteenth prime number, a safe prime,^[1] the thirteenth supersingular prime,^[2] the fourth isolated prime, and the sixth Lucas prime.^[3] Forty-seven is a highly cototient number.^[4] It is an Eisenstein prime with no imaginary part and real part of the form 3n − 1.

It is a Lucas number. It is also a Keith number because its digits appear as successive terms earlier in the series of Lucas numbers: 2, 1, 3, 4, 7, 11, 18, 29, 47, ...^[5]

It is the number of trees on 9 unlabeled nodes.^[6]

Forty-seven is a strictly non-palindromic number.^[7]

Its representation in binary being 101111, 47 is a prime Thabit number, and as such is related to the pair of amicable numbers {17296, 18416}.

In science

• 47 is the atomic number of silver.

In popular culture

Pomona College

The Smith Clock Tower (right) at Pomona College has been set up to chime on the 47th minute of the hour.

The number 47 has historical implications to Pomona College, a liberal arts college in Claremont, California, and has been incorporated into various aspects of campus life.^[10][11] The tradition began in the summer of 1964, when two students, Laurie Mets and Bruce Elgin, conducted a research project seeking to find out whether the number occurs more often in nature than would be expected by chance. They documented various 47 sightings, and professor Donald Bentley produced a false mathematical proof that 47 was equal to all other integers. The number became a meme among the class, which spread once the academic year began and snowballed over time.^[12]

Notable 47 sightings include the fact that Pomona is located off of exit 47 of Interstate 10, and the fact that the largest residential building on campus, Mudd-Blaisdell (formally Florence Carrier Blaisdell and Della Mullock Mudd Hall, a title with 47 characters), was completed in 1947 and contains a staircase with 47 balusters.^[12]

Many Pomona alumni have deliberately inserted 47 references into their work.^[10] Joe Menosky (class of 1979), a writer for Star Trek: The Next Generation, inserted 47 mentions into nearly every episode of the show, a practice that has been picked up by other Star Trek writers.^[12][13][14] Pomona hosts a community service–oriented celebration every April 7 (abbreviated 4/7 in the U.S.).^[15] In the early 2010s, the college's clock tower was set up to chime on the 47th minute of the hour.^[16][17]

Calendar years

• 47 BC
• AD 47

See also

• List of highways numbered 47

Other

• Telephone dialing country code for Norway
• The AK-47, also known as a Kalashnikov rifle, is one of the most widely used military weapons in the world.
• The CH-47 Chinook, a helicopter.
• 47 is the number of the French department Lot-et-Garonne.
• The P-47 Thunderbolt was a fighter plane in World War II.
• There are Forty-seven Ronin in the famous Japanese story.
• There are 47 Prefectures of Japan.
• The player protagonist of the Hitman video game franchise is called Agent 47.

References

Wikimedia Commons has media related to 47 (number).