| ||||
---|---|---|---|---|
Cardinal | ninety-one | |||
Ordinal | 91st (ninety-first) | |||
Factorization | 7 × 13 | |||
Divisors | 1, 7, 13, 91 | |||
Greek numeral | ϞΑ´ | |||
Roman numeral | XCI | |||
Binary | 10110112 | |||
Ternary | 101013 | |||
Senary | 2316 | |||
Octal | 1338 | |||
Duodecimal | 7712 | |||
Hexadecimal | 5B16 |
91 (ninety-one) is the natural number following 90 and preceding 92.
In mathematics
[edit]![](Https://upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Cube-sum-diff-91.png/200px-Cube-sum-diff-91.png)
91 is:
- the twenty-seventh distinct semiprime[1] and the second of the form (7.q), where q is a higher prime.
- the aliquot sum of 91 is 21 33; itself a semiprime, within an aliquot sequence of two composite numbers (91,21,11, 1,0) to the prime in the 11-aliquot tree. 91 is the fourth composite number in the 11-aliquot tree.(91,51,21,18).
- a triangular number.
- a hexagonal number,[2] one of the few such numbers to also be a centered hexagonal number.[3]
- a centered nonagonal number.[4]
- a centered cube number.[5]
- a square pyramidal number, being the sum of the squares of the first six integers.[6]
- 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):[7]
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.[8]
- a repdigit in base 9 (1119).
- palindromic in bases 3 (101013), 9 (1119), and 12 (7712).
- a Riordan number.[9]
- the smallest number that looks prime but isn't, proven using the Rotten Theorem by John Conway.[10][11]
The decimal equivalent of the fraction 1⁄91 can be obtained by using powers of 9.
In science
[edit]- 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
[edit]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.
- STS-91 Space Shuttle Discovery mission to the International Space Station, June 2, 1998
- Swedish comic strip 91:an
- The 91st Missile 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
References
[edit]- ^ Sloane, N. J. A. (ed.). "Sequence A001358". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
- ^ "Sloane's A000384 : Hexagonal numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
- ^ "Sloane's A003215 : Hex (or centered hexagonal) numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
- ^ "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.
- ^ "Sloane's A005898 : Centered cube numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
- ^ "Sloane's A000330 : Square pyramidal numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
- ^ Sloane, N. J. A. (ed.). "Sequence A047696 (Smallest positive number that can be written in n ways as a sum of two (not necessarily positive) cubes.)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
- ^ Friedman, Erich. What's Special About This Number? Archived 2018-02-23 at the Wayback Machine
- ^ "Sloane's A005043 : Riordan numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
- ^ "John Conway proves that 91 is the smallest number which looks prime but isn't". Ryan Andersen. Retrieved 2024-05-09.
- ^ "Prime Numbers".
Well, that’s interesting to know that Psilotum nudum are known as whisk ferns. Psilotum nudum is the commoner species of the two. While the P. flaccidum is a rare species and is found in the tropical islands. Both the species are usually epiphytic in habit and grow upon tree ferns. These species may also be terrestrial and grow in humus or in the crevices of the rocks.
View the detailed Guide of Psilotum nudum: Detailed Study Of Psilotum Nudum (Whisk Fern), Classification, Anatomy, Reproduction