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91 (number) Contents In mathematics In science In other fields References Navigation menuobject"Sloane's A000384 : Hexagonal numbers""Sloane's A003215 : Hex (or centered hexagonal) numbers""Sloane's A060544 : Centered 9-gonal (also known as nonagonal or enneagonal) numbers""Sloane's A005898 : Centered cube numbers""Sloane's A000330 : Square pyramidal numbers"What's Special About This Number?e

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Integers


natural number9092












91 (number)




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Natural number




































← 90 91 92 →

← 90 91 92 93 94 95 96 97 98 99 →

List of numbers — Integers


← 0 10 20 30 40 50 60 70 80 90 →

Cardinalninety-one
Ordinal91st
(ninety-first)
Factorization7 × 13
Divisors1, 7, 13, 91
Greek numeralϞΑ´
Roman numeralXCI
Binary10110112
Ternary101013
Quaternary11234
Quinary3315
Senary2316
Octal1338
Duodecimal7712
Hexadecimal5B16
Vigesimal4B20
Base 362J36

91 (ninety-one) is the natural number following 90 and preceding 92.






Contents





  • 1 In mathematics


  • 2 In science


  • 3 In other fields


  • 4 References




In mathematics


91 is:


  • the twenty-seventh distinct semiprime and the second of the form (7.q).

  • a triangular number.

  • a hexagonal number,[1] one of the few such numbers to also be a centered hexagonal number.[2]

  • a centered nonagonal number.[3]

  • a centered cube number.[4]

  • a square pyramidal number, being the sum of the squares of the first six integers.[5]

  • the smallest positive integer expressible as a sum of two cubes in two different ways if negative roots are allowed (alternatively the sum of two cubes and the difference of two cubes): 91 = 63 + (−5)3 = 43 + 33. (See 1729 for more details). This implies that 91 is the second cabtaxi number.

  • the smallest positive integer expressible as a sum of six distinct squares: 91 = 12 + 22 + 32 + 42 + 52 + 62. The only other ways to write 91 as a sum of distinct squares are: 91 = 12 + 42 + 52 + 72 and 91 = 12 + 32 + 92.

  • the smallest pseudoprime satisfying the congruence 3n ≡ 3 mod n.[6]

  • a repdigit in base 9 (1119).

  • palindromic in bases 3 (101013), 9 (1119), and 12 (7712).

  • the fourth composite number in the 11-aliquot tree. The aliquot sum of 91 is 21 within the aliquot sequence (91,21,11,1,0).

The decimal equivalent of the fraction ​1⁄91 can be obtained by using powers of 9.



In science


  • 91 is the atomic number of protactinium, an actinide.


  • McCarthy 91 function, a recursive function in discrete mathematics


  • Messier object M91, a magnitude 11.5 spiral galaxy in the constellation Coma Berenices

  • The New General Catalogue object NGC 91, a single star in the constellation Andromeda


In other fields


See also: List of highways numbered 91

Ninety-one is also:


  • The code for international direct dial phone calls to India

  • In cents of a U.S. dollar, the amount of money one has if one has one each of the coins of denominations less than a dollar (penny, nickel, dime, quarter and half dollar)

  • The ISBN Group Identifier for books published in Sweden.


  • Psalm 91 is known as the Psalm of Protection. It is also the title of a book by Peggy Joyce Ruth

  • 91 is a solitaire card game where the object is to move cards, so the top cards total 91.


  • STS-91 Space Shuttle Discovery mission to the International Space Station, June 2, 1998


  • Swedish comic strip 91:an

  • The 91st Space Wing (91 SW) is a Minuteman (missile) III unit of the United States Air Force, based at Minot Air Force Base, North Dakota

  • The number of the French department Essonne


  • Ninety One or 91 is a Kazakhstan Q-pop boy band formed by JUZ Entertainment in 2014


References



  1. ^ "Sloane's A000384 : Hexagonal numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29..mw-parser-output cite.citationfont-style:inherit.mw-parser-output .citation qquotes:"""""""'""'".mw-parser-output .citation .cs1-lock-free abackground:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center.mw-parser-output .citation .cs1-lock-limited a,.mw-parser-output .citation .cs1-lock-registration abackground:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center.mw-parser-output .citation .cs1-lock-subscription abackground:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registrationcolor:#555.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration spanborder-bottom:1px dotted;cursor:help.mw-parser-output .cs1-ws-icon abackground:url("//upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Wikisource-logo.svg/12px-Wikisource-logo.svg.png")no-repeat;background-position:right .1em center.mw-parser-output code.cs1-codecolor:inherit;background:inherit;border:inherit;padding:inherit.mw-parser-output .cs1-hidden-errordisplay:none;font-size:100%.mw-parser-output .cs1-visible-errorfont-size:100%.mw-parser-output .cs1-maintdisplay:none;color:#33aa33;margin-left:0.3em.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-formatfont-size:95%.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-leftpadding-left:0.2em.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-rightpadding-right:0.2em


  2. ^ "Sloane's A003215 : Hex (or centered hexagonal) numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.


  3. ^ "Sloane's A060544 : Centered 9-gonal (also known as nonagonal or enneagonal) numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.


  4. ^ "Sloane's A005898 : Centered cube numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.


  5. ^ "Sloane's A000330 : Square pyramidal numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.


  6. ^ Friedman, Erich. What's Special About This Number?










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