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47 (number)

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Subject: List of prime numbers, 46 (number), 48 (number), 43 (number), Thabit number
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47 (number)

46 47 48
Cardinal forty-seven
Ordinal 47th
Factorization prime
Divisors 1, 47
Roman numeral XLVII
Binary 1011112
Ternary 12023
Quaternary 2334
Quinary 1425
Senary 1156
Octal 578
Duodecimal 3B12
Hexadecimal 2F16
Vigesimal 2720
Base 36 1B36

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


  • In mathematics 1
  • In science 2
    • Astronomy 2.1
  • As an in-joke 3
  • Calendar years 4
  • Other 5
  • References 6
  • External links 7

In mathematics

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

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

Forty-seven is a strictly non-palindromic number.

Its representation in binary being 00101111, 47 is a prime Thabit number, and as such is related to the pair of amicable numbers {17296, 18416}.

Forty-seven is a Carol number.

In science


As an in-joke

Forty-seven has been the favorite number of Pomona College, California, USA, since 1964. A mathematical proof, written in 1964 by Professor Donald Bentley, supposedly demonstrates that all numbers are equal to 47.[5] However, Bentley offered it as a "joke proof" to further a popular student research project that listed real and imaginative "47 sightings". Bentley used the invalid proof to introduce his students to the concept of mathematical proofs.[6] The proof used limits to show that the sum of the two equal sides of an isosceles triangle is equal to the base side. Bentley chose forty-seven as the base side, but he could have used any number.

Joe Menosky graduated from Pomona College in 1979 and went on to become one of the story writers of Star Trek: The Next Generation. Menosky "infected" other Star Trek writers with an enthusiasm for the number 47.[7] As a result, 47, its reverse 74, its multiples, or combinations of 47 occur surreptitiously in almost every episode of the program and its spin-offs Star Trek: Deep Space Nine, Star Trek: Voyager and Star Trek: Enterprise.[5][8] Forty-seven might be mentioned in dialogue or appear on a computer screen, for example:

  • In the TNG episode "Darmok", the computer of the Enterprise reports to have found 47 occurrences of the word "Darmok" in its database.
  • In Star Trek Generations, Scotty manages to beam up only 47 El-Aurians before their ship is destroyed by the energy ribbon.
  • In the DS9 episode "Whispers", the planet Parada 4 has seven moons.
  • In the Voyager episode "Parallax", we learn that the Emergency Medical Holographic Channel is 47 and that the EMH has the experience of 47 individual medical officers.
  • In the Voyager episode "Non Sequitur", Harry Kim lives in apartment 4-G, G being the seventh letter of the alphabet. The intentionality of this reference to 47 was confirmed by Brannon Braga, the writer of that episode.[9]
  • In the 2009 film Star Trek, the Enterprise was built in Sector 47 of the Riverside Shipyards, and 47 Klingon ships are said to have been destroyed by Nero's ship, the Narada.

J. J. Abrams, who produced and directed Star Trek, frequently uses the number 47 in his productions, including episodes of his TV series Fringe. In the Season 1 episode "Bad Dreams", aired shortly before the release of Star Trek in theaters, Nick Lane's bulletin board features a large centrally-located sheet of paper with only the number 47 in huge typeface. It recurs in the series, for example 47 minutes being the maximum amount of time for a time chamber in the series to last, and there being exactly 47 shapeshifters. J.J. Abrams continues to incorporate 47 into movies and series he produces and directs. There are many 47's in Fringe, Alias, and recently in Revolution, of which Abrams is a producer. In the Season 1 episode "Soul Train" of the series Revolution, the characters are involved with an old train engine where the engine number happens to be 47.[10]

Calendar years



  1. ^ [1]
  2. ^ The NGC / IC Project - Home of the Historically Corrected New General Catalogue (HCNGC) since 1993
  3. ^ Internet Archive Wayback Machine
  4. ^ NASA - Lunar Eclipses of Saros Series 1 to 175
  5. ^ a b "The Mystique of 47". Pomona College (via  
  6. ^ "The Mystery of 47". Pomona College. Retrieved 2007-08-29. 
  7. ^ "Stardate 47". Pomona College (via  
  8. ^ "Starbase Pomona". Pomona College (via  
  9. ^ A letter from Brannon Braga
  10. ^ Roco. "Revolution Observations: 1.05 Soul Train". Retrieved 28 April 2013. 

External links

  • Frequently Asked Questions about 47 and The 47 Society
  • Pomona College's Star Trek Connection
  • Star Trek Voyager and the Number 47 - Featurette
  • 47 in the Alias fandom (from the All Alias Guide)
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