Fibonacci number: Difference between revisions

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{{redirect|Fibonacci Sequence|the chamber ensemble|Fibonacci Sequence (ensemble)}}
{{redirect|Fibonacci Sequence|the chamber ensemble|Fibonacci Sequence (ensemble)}}
[[File:Fibonacci Squares.svg|thumb|300x300px|A tiling with squares whose side lengths are successive Fibonacci numbers: 1, 1, 2, 3, 5, 8, 13 and 21.]]
[[File:Fibonacci Squares.svg|thumb|300x300px|A tiling with squares whose side lengths are successive Fibonacci numbers: 1, 1, 2, 3, 5, 8, 13 and 21.]]
In mathematics, the '''Fibonacci numbers''', commonly denoted {{math|''F<sub>n</sub>''}}, form a [[integer sequence|sequence]], the '''Fibonacci sequence''', in which each number is the sum of the two preceding ones. The sequence commonly starts from 0 and 1, although some authors omit the initial terms and start the sequence from 1 and 1 or from 1 and 2.
In mathematics, the '''Fibonacci numbers''', commonly denoted {{nowrap|{{math|''F<sub>n</sub>''}}{{space|hair}}}}, form a [[integer sequence|sequence]], the '''Fibonacci sequence''', in which each number is the sum of the two preceding ones. The sequence commonly starts from 0 and 1, although some authors omit the initial terms and start the sequence from 1 and 1 or from 1 and 2.
Starting from 0 and 1, the next few values in the sequence are:<ref name=oeis>{{Cite OEIS|1=A000045|mode=cs2}}</ref>
Starting from 0 and 1, the next few values in the sequence are:<ref name=oeis>{{Cite OEIS|1=A000045|mode=cs2}}</ref>
:0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, ...
:0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, ...
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* At the end of the first month, they mate, but there is still only 1 pair.
* At the end of the first month, they mate, but there is still only 1 pair.
* At the end of the second month they produce a new pair, so there are 2 pairs in the field.[[File:Liber abbaci magliab f124r.jpg|thumb|A page of [[Fibonacci]]'s ''[[Liber Abaci]]'' from the [[National Central Library (Florence)|Biblioteca Nazionale di Firenze]] showing (in box on right) the Fibonacci sequence with the position in the sequence labeled in Latin and Roman numerals and the value in Hindu-Arabic numerals.|367x367px]]
* At the end of the second month they produce a new pair, so there are 2 pairs in the field.[[File:Liber abbaci magliab f124r.jpg|thumb|A page of [[Fibonacci]]'s ''[[Liber Abaci]]'' from the [[National Central Library (Florence)|Biblioteca Nazionale di Firenze]] showing (in box on right) the Fibonacci sequence with the position in the sequence labeled in Latin and Roman numerals and the value in Hindu-Arabic numerals.|367x367px]]
* At the end of the third month, the original pair produce a second pair, but the second pair only mate without breeding, so there are 3 pairs in all.
* At the end of the third month, the original pair produce a second pair, but the second pair only mate to gestate for a month, so there are 3 pairs in all.
* At the end of the fourth month, the original pair has produced yet another new pair, and the pair born two months ago also produces their first pair, making 5 pairs.
* At the end of the fourth month, the original pair has produced yet another new pair, and the pair born two months ago also produces their first pair, making 5 pairs.


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where
where
<math display=block>\varphi = \frac{1 + \sqrt{5}}{2} \approx 1.61803\,39887\ldots</math>
<math display=block>\varphi = \frac{1 + \sqrt{5}}{2} \approx 1.61803\,39887\ldots</math>
is the [[golden ratio]] ({{OEIS2C|id=A001622}}), while {{mvar|ψ}} is its [[Conjugate_(square_roots)|conjugate]], which both display [[Golden_ratio_conjugate|the unique properties of the golden ratio]], as −{{mvar|ψ}} is also the [[Multiplicative_inverse|inverse]] of {{mvar|φ}} and its decimal part over 1 at the same time:{{Sfn | Ball | 2003 | p = 156}}
is the [[golden ratio]], and {{mvar|ψ}} is its [[Conjugate (square roots)|conjugate]]:{{Sfn | Ball | 2003 | p = 156}}
<math display=block>\psi = \frac{1 - \sqrt{5}}{2} = 1 - \varphi = - {1 \over \varphi} \approx -0.61803\,39887\ldots.</math>
<math display=block>\psi = \frac{1 - \sqrt{5}}{2} = 1 - \varphi = - {1 \over \varphi} \approx -0.61803\,39887\ldots.</math>


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