← 46 47 48 →
Cardinalforty-seven
Ordinal47th
(forty-seventh)
Factorizationprime
Prime15th
Divisors1, 47
Greek numeralΜΖ´
Roman numeralXLVII
Binary1011112
Ternary12023
Senary1156
Octal578
Duodecimal3B12

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 popular culture

Pomona College

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]

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. Archived 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. ^
9. ^ The NGC / IC Project – Home of the Historically Corrected New General Catalogue (HCNGC) since 1993
10. ^ a b Lipka, Sara (11 February 2005). "Pomona's Prime Number". The Chronicle of Higher Education. Archived from the original on October 29, 2020. Retrieved 7 April 2020.
11. ^ "1964". Pomona College Timeline. Pomona College. Archived from the original on August 7, 2020. Retrieved 7 April 2020.
12. ^ a b c Dolinar, Sarah (October 1, 2000). "The Mystery of 47". Pomona College Magazine. Vol. 37, no. 1. Pomona College. Archived 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. Archived 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. Archived 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. Archived 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. Archived from the original on July 31, 2019. Retrieved 7 April 2019.
18. ^ "Capital Steez: King Capital". The Fader. Rosenberg, Eli. Retrieved 2016-08-30.