47 (number)

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

← 46 47 48 →
← 40 41 42 43 44 45 46 47 48 49 → List of numbers Integers ← 0 10 20 30 40 50 60 70 80 90 →
Cardinal	forty-seven
Ordinal	47th (forty-seventh)
Factorization	prime
Prime	15th
Divisors	1, 47
Greek numeral	ΜΖ´
Roman numeral	XLVII
Binary	1011112
Ternary	12023
Senary	1156
Octal	578
Duodecimal	3B12
Hexadecimal	2F16

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.

Astronomy

• The 47-year cycle of Mars: after 47 years – 22 synodic periods of 780 days each – Mars returns to the same position among the stars and is in the same relationship to the Earth and Sun. The ancient Mesopotamians discovered this cycle.^[8]
• Messier object M47, a magnitude 4.5 open cluster in the constellation Puppis
• 47 Tucanae, the second brightest globular cluster in the sky, located in the constellation Tucana.
• The New General Catalogue object NGC 47,^[9] a barred spiral galaxy in the constellation Cetus. This object is also designated as NGC 58.

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]

Other

Agent 47 is the protagonist of the Hitman video game, movie and comic book franchise.

Late rapper Capital Steez was infatuated with the number 47 and what it meant spiritually. He believed the number 47 was the "perfect expression of balance in the world", representing the tension between the heart and the brain (the fourth and sixth chakra, respectively.) The number featured on the cover of AmeriKKKan Korruption, stylized to resemble a swastika.^[18]

Calendar years

• 47 BC
• AD 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.

References

1. "Sloane's A005385 : Safe primes". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30.
2. "Sloane's A002267 : The 15 supersingular primes". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30.
3. "Sloane's A005479 : Prime Lucas numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30.
4. "Sloane's A100827 : Highly cototient numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30.
5. "Sloane's A007629 : Repfigit (REPetitive FIbonacci-like diGIT) numbers (or Keith numbers)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30.
6. "Sloane's A000055: Number of trees with n unlabeled nodes". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. from the original on 2010-11-29. Retrieved 2021-12-19.
7. "Sloane's A016038 : Strictly non-palindromic numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30.
8. "Astronomy 100 – Early Astronomy".
9. The NGC / IC Project – Home of the Historically Corrected New General Catalogue (HCNGC) since 1993
10. Lipka, Sara (11 February 2005). "Pomona's Prime Number". The Chronicle of Higher Education. from the original on October 29, 2020. Retrieved 7 April 2020.
11. "1964". Pomona College Timeline. Pomona College. from the original on August 7, 2020. Retrieved 7 April 2020.
12. Dolinar, Sarah (October 1, 2000). "The Mystery of 47". Pomona College Magazine. Vol. 37, no. 1. Pomona College. from the original on October 26, 2020. Retrieved 7 April 2020.
13. Shin, Daniel (September 7, 2016). "Let's do the number: 'Star Trek' and the 47 conspiracy". Marketplace. American Public Media. from the original on October 1, 2020. Retrieved 7 April 2020.
14. Klein, Ezra (November 21, 2012). "The Last Word". The Last Word with Lawrence O'Donnell. NBCUniversal. 56 minutes in. MSNBC. Retrieved April 7, 2021 – via Archive.org.
15. "4/7 Celebration of Sagehen Impact". Pomona College. from the original on July 31, 2019. Retrieved 7 April 2019.
16. Rowan, Brendan (November 5, 2010). "Clock Tower Bell Set to Chime On the 47th Minute". The Student Life. from the original on July 31, 2019. Retrieved 7 April 2019.
17. "Tower's bell ringing again at Pomona College". Los Angeles Daily News. November 7, 2010. from the original on July 31, 2019. Retrieved 7 April 2019.
18. "Capital Steez: King Capital". The Fader. Rosenberg, Eli. Retrieved 2016-08-30.

 

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